Micromachined piezoelectric x-axis gyroscope

ABSTRACT

A method of fabricating a gyroscope may involve depositing conductive material on a substrate, forming an anchor on the substrate, forming a drive frame on the anchor and forming pairs of drive beams on opposing sides of the anchor. The drive beams may be configured to constrain the drive frame to rotate substantially in the plane of the drive beams. The method may involve forming a proof mass around the drive frame and forming a plurality of sense beams that connect the drive frame to the proof mass. The sense beams may be tapered sense beams having a width that decreases with increasing distance from the anchor. The tapered sense beams may be configured to allow sense motions of the proof mass in a sense plane substantially perpendicular to the plane of the drive beams in response to an applied angular rotation. Some components may be formed from plated metal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to, and is a divisional application of,U.S. patent application Ser. No. 12/930,186, filed Dec. 30, 2010,entitled “MICROMACHINED PIEZOELECTRIC X-AXIS GYROSCOPE” and assigned tothe assignee hereof, which has issued as U.S. Pat. No. 8,584,522. Thisapplication claims priority to U.S. Provisional Patent Application No.61/343,598, filed Apr. 30, 2010, entitled “MICROMACHINED PIEZOELECTRICX-AXIS GYROSCOPE” and assigned to the assignee hereof. This applicationalso claims priority to U.S. Provisional Patent Application No.61/343,599, filed Apr. 30, 2010, entitled “MICROMACHINED PIEZOELECTRICZ-AXIS GYROSCOPE” and assigned to the assignee hereof. This applicationalso claims priority to U.S. Provisional Patent Application No.61/343,601, filed Apr. 30, 2010, entitled “STACKED LATERAL OVERLAPTRANSDUCER (SLOT) BASED 3-AXIS MEMS ACCELEROMETER” and assigned to theassignee hereof. This application also claims priority to U.S.Provisional Patent Application No. 61/343,600, filed Apr. 30, 2010,entitled “MICROMACHINED PIEZOELECTRIC X-AXIS & Z-AXIS GYROSCOPE ANDSTACKED LATERAL OVERLAP TRANSDUCER (SLOT) BASED 3-AXIS MEMSACCELEROMETER” and assigned to the assignee hereof. These priorapplications are considered part of, and are hereby incorporated byreference in, this application.

This application is related to U.S. patent application Ser. No.12/930,174, entitled “MICROMACHINED PIEZOELECTRIC X-AXIS GYROSCOPE” andfiled on Dec. 30, 2010, and is also related to U.S. patent applicationSer. No. 12/930,175, entitled “MICROMACHINED PIEZOELECTRIC Z-AXISGYROSCOPE” and filed on Dec. 30, 2010, and is also related to U.S.patent application Ser. No. 12/930,187, entitled “STACKED LATERALOVERLAP TRANSDUCER (SLOT) BASED THREE-AXIS ACCELEROMETER” and filed onDec. 30, 2010, and is also related to U.S. patent application Ser. No.12/930,229, entitled “MICROMACHINED PIEZOELECTRIC THREE-AXIS GYROSCOPEAND STACKED LATERAL OVERLAP TRANSDUCER (SLOT) BASED THREE-AXISACCELEROMETER” and filed on Dec. 30, 2010, all of which are herebyincorporated by reference and for all purposes.

TECHNICAL FIELD

This disclosure relates to electromechanical systems, and morespecifically to multi-axis gyroscopes and accelerometers.

DESCRIPTION OF THE RELATED TECHNOLOGY

Electromechanical systems include devices having electrical andmechanical elements, actuators, transducers, sensors, optical components(e.g., mirrors) and electronics. Electromechanical systems can bemanufactured at a variety of scales including, but not limited to,microscales and nanoscales. For example, microelectromechanical systems(MEMS) devices can include structures having sizes ranging from about amicron to hundreds of microns or more. Nanoelectromechanical systems(NEMS) devices can include structures having sizes smaller than a micronincluding, for example, sizes smaller than several hundred nanometers.Electromechanical elements may be created using deposition, etching,lithography, and/or other micromachining processes that etch away partsof substrates and/or deposited material layers, or that add layers toform electrical and electromechanical devices.

One type of electromechanical systems device is called aninterferometric modulator (IMOD). As used herein, the terminterferometric modulator or interferometric light modulator refers to adevice that selectively absorbs and/or reflects light using theprinciples of optical interference. In some implementations, aninterferometric modulator may include a pair of conductive plates, oneor both of which may be transparent and/or reflective, wholly or inpart, and capable of relative motion upon application of an appropriateelectrical signal. In an implementation, one plate may include astationary layer deposited on a substrate and the other plate mayinclude a reflective membrane separated from the stationary layer by anair gap. The position of one plate in relation to another can change theoptical interference of light incident on the interferometric modulator.Interferometric modulator devices have a wide range of applications, andare anticipated to be used in improving existing products and creatingnew products, especially those with display capabilities.

Recently, there has been increased interest in fabricating small-scalegyroscopes and accelerometers. For example, some gyroscopes and/oraccelerometers have been incorporated into mobile devices, such asmobile display devices. Although such gyroscopes and accelerometers aresatisfactory in some respects, it would be desirable to provide improvedsmall-scale gyroscopes and accelerometers.

SUMMARY

The systems, methods and devices of the disclosure each have severalinnovative aspects, no single one of which is solely responsible for thedesirable attributes disclosed herein.

One innovative aspect of the subject matter described in this disclosurecan be implemented in a gyroscope that includes a drive frame, a centralanchor and a plurality of drive beams disposed on opposing sides of thecentral anchor. The drive beams may connect the drive frame to thecentral anchor. Each of the drive beams may include a piezoelectriclayer. Each the drive beams may be configured to cause the drive frameto oscillate torsionally in a plane of the drive beams.

The gyroscope may also include a proof mass and a plurality of sensebeams. At least some components of the gyroscope (such as the proofmass) may be formed, at least in part, from plated metal. The sensebeams may include piezoelectric sense electrodes. The sense beams may beconfigured for connecting the drive frame to the proof mass. The sensebeams may be configured to bend in a sense plane substantiallyperpendicular to the plane of the drive beams in response to an appliedangular rotation, causing a piezoelectric charge in the senseelectrodes.

The drive frame may be disposed within the proof mass. The plurality ofdrive beams may be further configured to constrain the drive frame torotate substantially in the plane of the drive beams.

The plurality of drive beams may include a first pair of drive beamsdisposed on a first side of the central anchor and a second pair ofdrive beams disposed on an opposing side of the central anchor. Thefirst pair of drive beams and the second pair of drive beams may beconfigured to generate drive oscillations via a differentialpiezoelectric drive.

The sense beams may be configured to bend in the sense plane in responseto sense motion of the proof mass. The drive frame may be substantiallydecoupled from the sense motion of the proof mass.

The sense beams may be tapered sense beams having a width that decreaseswith increasing distance from the anchor. Bending stresses along thetapered sense beams may be substantially uniform with increasingdistance from the anchors when the gyroscope is operating in a sensemode. The sense beams may be loaded due to forces exerted by the drivebeams.

Some methods of fabricating a gyroscope provided herein involvedepositing electrodes on a substrate, forming an anchor on thesubstrate, forming a drive frame on the anchor and forming pairs ofdrive beams on opposing sides of the anchor. The drive beams may connectthe drive frame to the anchor. The drive beams may be configured toconstrain the drive frame to rotate substantially in the plane of thedrive beams.

The method may also involve forming a proof mass around the drive frameand forming a plurality of sense beams that connect the drive frame tothe proof mass. The sense beams may be configured to allow sense motionsof the proof mass in a sense plane substantially perpendicular to theplane of the drive beams in response to an applied angular rotation. Thesense beams may also be configured to substantially decouple the sensemotions of the proof mass means from motions of the drive frame.

The process of forming the drive beams may include the following:depositing a first metal layer that is in contact with the electrodes;depositing a piezoelectric layer on the first metal layer; depositing asecond metal layer on the piezoelectric layer; and electroplating athird metal layer on the second metal layer. The process of forming theanchor may involve etching through a sacrificial layer to expose thefirst metal layer, depositing an oxide layer on the first metal layer;forming a seed layer on the oxide layer and electroplating the thirdmetal layer on the seed layer. The method may also involve separatingthe substrate into a plurality of sub-panels prior to theelectroplating.

Forming the proof mass and forming the drive frame may involve thefollowing processes: etching between a drive frame area and a proof massarea; depositing high aspect ratio photoresist material between thedrive frame area and the proof mass area; and electroplating the thirdmetal layer in the drive frame area and the proof mass area. Forming theproof mass and forming the drive frame may also involve removing thehigh aspect ratio photoresist material from between the drive frame areaand the proof mass area, etching to expose a sacrificial layer disposedbelow the drive frame and the proof mass, and removing the sacrificiallayer to release the drive frame and the proof mass.

Alternative gyroscope implementations are described herein. Some suchgyroscopes include a central anchor and a proof mass disposed around thecentral anchor. The proof mass may have a first end and a second end.The gyroscope may include a first drive beam for connecting a first sideof the central anchor to the first end of the proof mass and a seconddrive beam for connecting a second side of the central anchor to thesecond end of the proof mass. A first pair of piezoelectric driveelectrodes may be disposed on the first drive beam and a second pair ofpiezoelectric drive electrodes may be disposed on the second drive beam.

The gyroscope may include sense electrodes, such as piezoelectric senseelectrodes. The sense electrodes may be disposed on the proof mass.Alternatively, or additionally, a first sense electrode may be disposedon the first drive beam and a second piezoelectric sense electrode maybe disposed on the second drive beam. The first pair and the second pairof drive electrodes may be configured to cause the proof mass tooscillate torsionally in a plane of the drive beams. For example, thefirst pair and the second pair of drive electrodes may be configured tocause the proof mass to oscillate torsionally via a differentialpiezoelectric drive.

The proof mass and/or the drive beams may be formed, at least in part,from plated metal. The proof mass may be configured for sense motionswherein the proof mass means bends in a sense plane in response to anapplied angular rotation. The sense plane may be substantiallyperpendicular to the plane of the drive beams. Each of the driveelectrodes and the sense electrodes may include a piezoelectric film.The sense motions of the proof mass may causing a piezoelectric chargein sense electrodes.

The first drive beam and/or the second drive beam may include a centralslot. Pairs of drive electrodes may be disposed on opposite sides of thecentral slot.

In some implementations, the apparatus may also include a display, aprocessor and a memory device. The processor may be configured tocommunicate with the display and the gyroscope(s). The processor may beconfigured to process image data and gyroscope data. The memory devicemay be configured to communicate with the processor. The apparatus mayalso include an input device configured to receive input data and tocommunicate the input data to the processor. The apparatus may alsoinclude a driver circuit configured to send at least one signal to thedisplay. The apparatus may also include a controller configured to sendat least a portion of the image data to the driver circuit. Theapparatus may also include an image source module configured to send theimage data to the processor. The image source module may include atleast one of a receiver, transceiver, and transmitter.

Details of one or more implementations of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages will becomeapparent from the description, the drawings, and the claims. Note thatthe relative dimensions of the following figures may not be drawn toscale.

BRIEF DESCRIPTION OF THE DRAWINGS

Statement Pursuant to 37 C.F.R. §1.84(a)(2)(iii):

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

FIG. 1 shows an example of an isometric view depicting two adjacentpixels in a series of pixels of an interferometric modulator (IMOD)display device.

FIG. 2 shows an example of a system block diagram illustrating anelectronic device incorporating a 3×3 interferometric modulator display.

FIG. 3 shows an example of a diagram illustrating movable reflectivelayer position versus applied voltage for the interferometric modulatorof FIG. 1.

FIG. 4 shows an example of a table illustrating various states of aninterferometric modulator when various common and segment voltages areapplied.

FIG. 5A shows an example of a diagram illustrating a frame of displaydata in the 3×3 interferometric modulator display of FIG. 2.

FIG. 5B shows an example of a timing diagram for common and segmentsignals that may be used to write the frame of display data illustratedin FIG. 5A.

FIG. 6A shows an example of a partial cross-section of theinterferometric modulator display of FIG. 1.

FIGS. 6B-6E show examples of cross-sections of varying implementationsof interferometric modulators.

FIG. 7 shows an example of a flow diagram illustrating a manufacturingprocess for an interferometric modulator.

FIGS. 8A-8E show examples of cross-sectional schematic illustrations ofvarious stages in a method of making an interferometric modulator.

FIGS. 9A and 9B show examples of the drive and sense modes of asingle-ended tuning-fork gyroscope.

FIG. 10A shows an example of a gyroscope having a proof mass suspendedby drive beams attached to a central anchor.

FIG. 10B shows an example of a gyroscope implementation similar to thatof FIG. 10A, but having a gap between the drive electrodes.

FIG. 11A shows an example of a drive mode of a gyroscope implementationsuch as that shown in FIG. 10A.

FIG. 11B shows an example of a sense mode of a gyroscope implementationbeing driven as shown in FIG. 11A.

FIG. 12 shows an example of a drive frame gyroscope implementation inwhich a drive frame is attached to a central anchor via drive beams.

FIG. 13A shows an example of a cross-section of a gyroscopeimplementation such as that shown in FIG. 12.

FIG. 13B shows an example of an enlarged pair of drive beams of thegyroscope implementation shown in FIG. 13A.

FIG. 14A shows an example of a drive mode of a gyroscope implementationsuch as that shown in FIG. 12.

FIG. 14B shows an example of a sense mode of a gyroscope implementationbeing driven as shown in FIG. 14A.

FIG. 15 shows an example of a sense frame gyroscope implementation.

FIG. 16A shows an example of a drive mode of the gyroscopeimplementation shown in FIG. 15.

FIG. 16B shows an example of a sense mode of the gyroscopeimplementation being driven as shown in FIG. 16A.

FIG. 17 shows an example of an alternative sense frame gyroscopeimplementation having tapered sense beams.

FIG. 18 shows an example of a finite element analysis superimposed upona gyroscope implementation such as that of FIG. 17, showingsubstantially uniform stresses on the tapered sense beams when operatingin a sense mode.

FIG. 19 shows an example of a plot of the stress level on the taperedsense beams versus the distance from the center for a gyroscopeimplementation such as that of FIG. 17.

FIG. 20A shows an example of a plan view of a z-axis gyroscopeimplementation.

FIG. 20B shows an example of an enlarged view of the drive beams of thez-axis gyroscope implementation shown in FIG. 20A.

FIG. 21A shows an example of a drive mode of a z-axis gyroscopeimplementation such as that depicted in FIG. 20A.

FIG. 21B shows an example of a sense mode of a z-axis gyroscopeimplementation driven as depicted in FIG. 20A.

FIG. 22 shows an example of a close-up view of one implementation of atapered sense beam from a z-axis gyroscope.

FIG. 23 shows an example of an electrode array that may be configured toapply corrective electrostatic forces to fine-tune the vibrational modeshapes of a proof mass.

FIG. 24 shows an example of an accelerometer for measuring in-planeacceleration.

FIG. 25 shows components of an example of an accelerometer for measuringout-of-plane acceleration.

FIG. 26A shows components of an example of an accelerometer formeasuring in-plane acceleration.

FIG. 26B shows an example of the response of the accelerometer of FIG.26A to acceleration along a first axis.

FIG. 26C shows an example of the response of the accelerometer of FIG.26A to acceleration along a second axis.

FIG. 26D shows an example of an accelerometer for measuring in-plane andout-of-plane acceleration.

FIG. 27 shows an example of an accelerometer for measuring out-of-planeacceleration.

FIG. 28 shows an example of an alternative accelerometer implementationfor measuring in-plane and out-of-plane acceleration.

FIG. 29 shows an example of another alternative accelerometerimplementation for measuring in-plane and out-of-plane acceleration.

FIG. 30 shows a graph depicting the relative sensitivity enabled byvarious materials that may be used to form an accelerometer or agyroscope.

FIG. 31A shows an example of a comb-finger accelerometer.

FIG. 31B shows a graph depicting the performance of comb drive andSLOT-based accelerometers.

FIG. 32 shows a graph depicting the performance of SLOT-basedaccelerometers having slots of various depths, including a through slot.

FIG. 33 shows an example of a flow diagram that outlines stages of amethod involving the use of one or more gyroscopes or accelerometers ina mobile device.

FIG. 34 shows an example of a flow diagram that provides an overview ofa method of fabricating accelerometers.

FIGS. 35A through 39B show examples of cross-sectional views of variousblocks in a process of fabricating accelerometers.

FIGS. 40A through 40C show examples of cross-sectional views of variousblocks in a process of forming a device that includes a MEMS die and anintegrated circuit.

FIG. 41 shows an example of a flow diagram that provides an overview ofa process of fabricating gyroscopes and related structures.

FIGS. 42A through 46B show examples of cross-sectional views through asubstrate, a portion of a gyroscope and portions of structures forpackaging the gyroscope and making electrical connections with thegyroscope, at various stages during the process outlined in FIG. 41.

FIGS. 47A and 47B show examples of system block diagrams illustrating adisplay device that includes a plurality of interferometric modulators,gyroscopes and/or accelerometers.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

The following detailed description is directed to certainimplementations for the purposes of describing the innovative aspects.However, the teachings herein can be applied in a multitude of differentways. The described implementations may be implemented in any devicethat is configured to display an image, whether in motion (e.g., video)or stationary (e.g., still image), and whether textual, graphical orpictorial. More particularly, it is contemplated that theimplementations may be implemented in or associated with a variety ofelectronic devices such as, but not limited to, mobile telephones,multimedia Internet enabled cellular telephones, mobile televisionreceivers, wireless devices, smartphones, bluetooth devices, personaldata assistants (PDAs), wireless electronic mail receivers, hand-held orportable computers, netbooks, notebooks, smartbooks, printers, copiers,scanners, facsimile devices, GPS receivers/navigators, cameras, MP3players, camcorders, game consoles, wrist watches, clocks, calculators,television monitors, flat panel displays, electronic reading devices(e.g., e-readers), computer monitors, auto displays (e.g., odometerdisplay, etc.), cockpit controls and/or displays, camera view displays(e.g., display of a rear view camera in a vehicle), electronicphotographs, electronic billboards or signs, projectors, architecturalstructures, microwaves, refrigerators, stereo systems, cassetterecorders or players, DVD players, CD players, VCRs, radios, portablememory chips, washers, dryers, washer/dryers, parking meters, packaging(e.g., MEMS and non-MEMS), aesthetic structures (e.g., display of imageson a piece of jewelry) and a variety of electromechanical systemsdevices. The teachings herein also can be used in non-displayapplications such as, but not limited to, electronic switching devices,radio frequency filters, sensors, accelerometers, gyroscopes,motion-sensing devices, magnetometers, inertial components for consumerelectronics, parts of consumer electronics products, varactors, liquidcrystal devices, electrophoretic devices, drive schemes, manufacturingprocesses and electronic test equipment. Thus, the teachings are notintended to be limited to the implementations depicted solely in theFigures, but instead have wide applicability as will be readily apparentto one having ordinary skill in the art.

This disclosure describes various types of inertial sensors, how suchsensors may be fabricated and how such sensors may be used. For example,some implementations described herein provide an x-axis gyroscope withlow quadrature and bias error. The gyroscope is well suited tomanufacturing on flat-panel display glass. Some such implementationsinclude a proof mass that can oscillate torsionally in-plane (about thez-axis) in the drive mode and torsionally out-of-plane in the sensemode. By changing its orientation within the plane, the gyroscope canfunction as a y-axis gyroscope. Additionally, by disposing the gyroscopein an orthogonal plane, the gyroscope can function as a z-axisgyroscope.

However, some implementations described herein provide a z-axisgyroscope that may be fabricated and/or disposed in the same plane asthe x-axis gyroscope and the y-axis gyroscope. Various z-axis gyroscopesdescribed herein also can have low quadrature and bias error. Someimplementations include a drive proof mass that may be piezoelectricallydriven in a substantially linear, x-directed motion (in-plane). Thedrive proof mass may be mechanically coupled to a sense proof mass,which vibrates torsionally in the presence of angular rotation about thez-axis. Motion of the sense proof mass can induce charge in apiezoelectric film on beams connecting the sense mass to a substrateanchor. The charge may be read out and processed electronically.

The proof masses can be made from a variety of materials such as thickplated-metal alloys (e.g., nickel-manganese (Ni—Mn)), single crystalsilicon from the device layer of a silicon on insulator (SOI) wafer,glass, and others. The piezoelectric film can be aluminum nitride (AlN),zinc oxide (ZnO), lead zirconate titanate (PZT), or other thin films, orsingle crystal materials such as quartz, lithium niobate, lithiumtantalate, and others. Some implementations are well suited formanufacturing on flat-panel display glass.

Various implementations described herein provide novel three-axisaccelerometers, as well as components thereof. Such three-axisaccelerometers have sizes, performance levels and costs that aresuitable for use in consumer electronic applications such as portablenavigation devices and smart phones. Some such implementations provide acapacitive stacked lateral overlap transducer (SLOT) based three-axisaccelerometer. Some implementations provide three-axis sensing using twoproof masses, whereas other implementations provide three-axis sensingusing only one proof mass. Different flexure types may be optimized foreach axis.

Particular implementations of the subject matter described in thisdisclosure can be implemented to realize one or more of the followingpotential advantages. For example, in some such implementations thex-axis gyroscopes, z-axis gyroscopes and/or SLOT-based three-axisaccelerometers may share layers that are deposited during a fabricationprocess. Combining such processes can enable the monolithic integrationof six inertial sensing axes on a single substrate, such as a singleglass substrate. Many implementations described herein may be fabricatedon large area glass panels. The fabrication processes that may be usedin forming SLOT-based three-axis accelerometers on large area glasspanels is compatible with processes for fabricating piezoelectricaluminum nitride (AlN) (or other piezoelectric materials) on platedmetal multi-axis MEMS gyroscopes, such as the x-axis, y-axis and z-axisgyroscopes described herein. Accordingly, some implementations describedherein involve fabricating x-axis gyroscopes, y-axis gyroscopes, z-axisgyroscopes and SLOT-based three-axis accelerometers on the same glasssubstrate.

One example of a suitable MEMS device, to which the describedimplementations may apply, is a reflective display device. Reflectivedisplay devices can incorporate interferometric modulators (IMODs) toselectively absorb and/or reflect light incident thereon usingprinciples of optical interference. IMODs can include an absorber, areflector that is movable with respect to the absorber, and an opticalresonant cavity defined between the absorber and the reflector. Thereflector can be moved to two or more different positions, which canchange the size of the optical resonant cavity and thereby affect thereflectance of the interferometric modulator. The reflectance spectrumsof IMODs can create fairly broad spectral bands which can be shiftedacross the visible wavelengths to generate different colors. Theposition of the spectral band can be adjusted by changing the thicknessof the optical resonant cavity, i.e., by changing the position of thereflector.

FIG. 1 shows an example of an isometric view depicting two adjacentpixels in a series of pixels of an interferometric modulator (IMOD)display device. The IMOD display device includes one or moreinterferometric MEMS display elements. In these devices, the pixels ofthe MEMS display elements can be in either a bright or dark state. Inthe bright (“relaxed,” “open” or “on”) state, the display elementreflects a large portion of incident visible light, e.g., to a user.Conversely, in the dark (“actuated,” “closed” or “off”) state, thedisplay element reflects little incident visible light. In someimplementations, the light reflectance properties of the on and offstates may be reversed. MEMS pixels can be configured to reflectpredominantly at particular wavelengths allowing for a color display inaddition to black and white.

The IMOD display device can include a row/column array of IMODs. EachIMOD can include a pair of reflective layers, i.e., a movable reflectivelayer and a fixed partially reflective layer, positioned at a variableand controllable distance from each other to form an air gap (alsoreferred to as an optical gap or cavity). The movable reflective layermay be moved between at least two positions. In a first position, i.e.,a relaxed position, the movable reflective layer can be positioned at arelatively large distance from the fixed partially reflective layer. Ina second position, i.e., an actuated position, the movable reflectivelayer can be positioned more closely to the partially reflective layer.Incident light that reflects from the two layers can interfereconstructively or destructively depending on the position of the movablereflective layer, producing either an overall reflective ornon-reflective state for each pixel. In some implementations, the IMODmay be in a reflective state when unactuated, reflecting light withinthe visible spectrum, and may be in a dark state when unactuated,reflecting light outside of the visible range (e.g., infrared light). Insome other implementations, however, an IMOD may be in a dark state whenunactuated, and in a reflective state when actuated. In someimplementations, the introduction of an applied voltage can drive thepixels to change states. In some other implementations, an appliedcharge can drive the pixels to change states.

The depicted portion of the pixel array in FIG. 1 includes two adjacentinterferometric modulators 12. In the IMOD 12 on the left (asillustrated), a movable reflective layer 14 is illustrated in a relaxedposition at a predetermined distance from an optical stack 16, whichincludes a partially reflective layer. The voltage V₀ applied across theIMOD 12 on the left is insufficient to cause actuation of the movablereflective layer 14. In the IMOD 12 on the right, the movable reflectivelayer 14 is illustrated in an actuated position near or adjacent theoptical stack 16. The voltage V_(bias) applied across the IMOD 12 on theright is sufficient to maintain the movable reflective layer 14 in theactuated position.

In FIG. 1, the reflective properties of pixels 12 are generallyillustrated with arrows 13 indicating light incident upon the pixels 12,and light 15 reflecting from the IMOD 12 on the left. Although notillustrated in detail, it will be understood by one having ordinaryskill in the art that most of the light 13 incident upon the pixels 12will be transmitted through the transparent substrate 20, toward theoptical stack 16. A portion of the light incident upon the optical stack16 will be transmitted through the partially reflective layer of theoptical stack 16, and a portion will be reflected back through thetransparent substrate 20. The portion of light 13 that is transmittedthrough the optical stack 16 will be reflected at the movable reflectivelayer 14, back toward (and through) the transparent substrate 20.Interference (constructive or destructive) between the light reflectedfrom the partially reflective layer of the optical stack 16 and thelight reflected from the movable reflective layer 14 will determine thewavelength(s) of light 15 reflected from the IMOD 12.

The optical stack 16 can include a single layer or several layers. Thelayer(s) can include one or more of an electrode layer, a partiallyreflective and partially transmissive layer and a transparent dielectriclayer. In some implementations, the optical stack 16 is electricallyconductive, partially transparent and partially reflective, and may befabricated, for example, by depositing one or more of the above layersonto a transparent substrate 20. The electrode layer can be formed froma variety of materials, such as various metals, for example indium tinoxide (ITO). The partially reflective layer can be formed from a varietyof materials that are partially reflective, such as various metals,e.g., chromium (Cr), semiconductors, and dielectrics. The partiallyreflective layer can be formed of one or more layers of materials, andeach of the layers can be formed of a single material or a combinationof materials. In some implementations, the optical stack 16 can includea single semi-transparent thickness of metal or semiconductor whichserves as both an optical absorber and conductor, while different, moreconductive layers or portions (e.g., of the optical stack 16 or of otherstructures of the IMOD) can serve to bus signals between IMOD pixels.The optical stack 16 also can include one or more insulating ordielectric layers covering one or more conductive layers or aconductive/absorptive layer.

In some implementations, the layer(s) of the optical stack 16 can bepatterned into parallel strips, and may form row electrodes in a displaydevice as described further below. As will be understood by one havingskill in the art, the term “patterned” is used herein to refer tomasking as well as etching processes. In some implementations, a highlyconductive and reflective material, such as aluminum (Al), may be usedfor the movable reflective layer 14, and these strips may form columnelectrodes in a display device. The movable reflective layer 14 may beformed as a series of parallel strips of a deposited metal layer orlayers (orthogonal to the row electrodes of the optical stack 16) toform columns deposited on top of posts 18 and an intervening sacrificialmaterial deposited between the posts 18. When the sacrificial materialis etched away, a defined gap 19, or optical cavity, can be formedbetween the movable reflective layer 14 and the optical stack 16. Insome implementations, the spacing between posts 18 may be on the orderof 1-1000 um, while the gap 19 may be on the order of <10,000 Angstroms(Å).

In some implementations, each pixel of the IMOD, whether in the actuatedor relaxed state, is essentially a capacitor formed by the fixed andmoving reflective layers. When no voltage is applied, the movablereflective layer 14 remains in a mechanically relaxed state, asillustrated by the IMOD 12 on the left in FIG. 1, with the gap 19between the movable reflective layer 14 and optical stack 16. However,when a potential difference, e.g., voltage, is applied to at least oneof a selected row and column, the capacitor formed at the intersectionof the row and column electrodes at the corresponding pixel becomescharged, and electrostatic forces pull the electrodes together. If theapplied voltage exceeds a threshold, the movable reflective layer 14 candeform and move near or against the optical stack 16. A dielectric layer(not shown) within the optical stack 16 may prevent shorting and controlthe separation distance between the layers 14 and 16, as illustrated bythe actuated IMOD 12 on the right in FIG. 1. The behavior is the sameregardless of the polarity of the applied potential difference. Though aseries of pixels in an array may be referred to in some instances as“rows” or “columns,” a person having ordinary skill in the art willreadily understand that referring to one direction as a “row” andanother as a “column” is arbitrary. Restated, in some orientations, therows can be considered columns, and the columns considered to be rows.Furthermore, the display elements may be evenly arranged in orthogonalrows and columns (an “array”), or arranged in non-linear configurations,for example, having certain positional offsets with respect to oneanother (a “mosaic”). The terms “array” and “mosaic” may refer to eitherconfiguration. Thus, although the display is referred to as including an“array” or “mosaic,” the elements themselves need not be arrangedorthogonally to one another, or disposed in an even distribution, in anyinstance, but may include arrangements having asymmetric shapes andunevenly distributed elements.

FIG. 2 shows an example of a system block diagram illustrating anelectronic device incorporating a 3×3 interferometric modulator display.The electronic device includes a processor 21 that may be configured toexecute one or more software modules. In addition to executing anoperating system, the processor 21 may be configured to execute one ormore software applications, including a web browser, a telephoneapplication, an email program, or other software application.

The processor 21 can be configured to communicate with an array driver22. The array driver 22 can include a row driver circuit 24 and a columndriver circuit 26 that provide signals to, e.g., a display array orpanel 30. The cross section of the IMOD display device illustrated inFIG. 1 is shown by the lines 1-1 in FIG. 2. Although FIG. 2 illustratesa 3×3 array of IMODs for the sake of clarity, the display array 30 maycontain a very large number of IMODs, and may have a different number ofIMODs in rows than in columns, and vice versa.

FIG. 3 shows an example of a diagram illustrating movable reflectivelayer position versus applied voltage for the interferometric modulatorof FIG. 1. For MEMS interferometric modulators, the row/column (i.e.,common/segment) write procedure may take advantage of a hysteresisproperty of these devices as illustrated in FIG. 3. An interferometricmodulator may require, for example, about a 10-volt potential differenceto cause the movable reflective layer, or mirror, to change from therelaxed state to the actuated state. When the voltage is reduced fromthat value, the movable reflective layer maintains its state as thevoltage drops back below, e.g., 10 volts, however, the movablereflective layer does not relax completely until the voltage drops below2 volts. Thus, a range of voltage, approximately 3 to 7 volts, as shownin FIG. 3, exists where there is a window of applied voltage withinwhich the device is stable in either the relaxed or actuated state. Thisis referred to herein as the “hysteresis window” or “stability window.”For a display array 30 having the hysteresis characteristics of FIG. 3,the row/column write procedure can be designed to address one or morerows at a time, such that during the addressing of a given row, pixelsin the addressed row that are to be actuated are exposed to a voltagedifference of about 10 volts, and pixels that are to be relaxed areexposed to a voltage difference of near zero volts. After addressing,the pixels are exposed to a steady state or bias voltage difference ofapproximately 5-volts such that they remain in the previous strobingstate. In this example, after being addressed, each pixel sees apotential difference within the “stability window” of about 3-7 volts.This hysteresis property feature enables the pixel design, e.g.,illustrated in FIG. 1, to remain stable in either an actuated or relaxedpre-existing state under the same applied voltage conditions. Since eachIMOD pixel, whether in the actuated or relaxed state, is essentially acapacitor formed by the fixed and moving reflective layers, this stablestate can be held at a steady voltage within the hysteresis windowwithout substantially consuming or losing power. Moreover, essentiallylittle or no current flows into the IMOD pixel if the applied voltagepotential remains substantially fixed.

In some implementations, a frame of an image may be created by applyingdata signals in the form of “segment” voltages along the set of columnelectrodes, in accordance with the desired change (if any) to the stateof the pixels in a given row. Each row of the array can be addressed inturn, such that the frame is written one row at a time. To write thedesired data to the pixels in a first row, segment voltagescorresponding to the desired state of the pixels in the first row can beapplied on the column electrodes, and a first row pulse in the form of aspecific “common” voltage or signal can be applied to the first rowelectrode. The set of segment voltages can then be changed to correspondto the desired change (if any) to the state of the pixels in the secondrow, and a second common voltage can be applied to the second rowelectrode. In some implementations, the pixels in the first row areunaffected by the change in the segment voltages applied along thecolumn electrodes, and remain in the state they were set to during thefirst common voltage row pulse. This process may be repeated for theentire series of rows, or alternatively, columns, in a sequentialfashion to produce the image frame. The frames can be refreshed and/orupdated with new image data by continually repeating this process atsome desired number of frames per second.

The combination of segment and common signals applied across each pixel(that is, the potential difference across each pixel) determines theresulting state of each pixel. FIG. 4 shows an example of a tableillustrating various states of an interferometric modulator when variouscommon and segment voltages are applied. As will be readily understoodby one having ordinary skill in the art, the “segment” voltages can beapplied to either the column electrodes or the row electrodes, and the“common” voltages can be applied to the other of the column electrodesor the row electrodes.

As illustrated in FIG. 4 (as well as in the timing diagram shown in FIG.5B), when a release voltage VC_(REL) is applied along a common line, allinterferometric modulator elements along the common line will be placedin a relaxed state, alternatively referred to as a released orunactuated state, regardless of the voltage applied along the segmentlines, i.e., high segment voltage VS_(H) and low segment voltage VS_(L).In particular, when the release voltage VC_(REL) is applied along acommon line, the potential voltage across the modulator (alternativelyreferred to as a pixel voltage) is within the relaxation window (seeFIG. 3, also referred to as a release window) both when the high segmentvoltage VS_(H) and the low segment voltage VS_(L) are applied along thecorresponding segment line for that pixel.

When a hold voltage is applied on a common line, such as a high holdvoltage VC_(HOLD) _(_) _(H) or a low hold voltage VC_(HOLD) _(_) _(L),the state of the interferometric modulator will remain constant. Forexample, a relaxed IMOD will remain in a relaxed position, and anactuated IMOD will remain in an actuated position. The hold voltages canbe selected such that the pixel voltage will remain within a stabilitywindow both when the high segment voltage VS_(H) and the low segmentvoltage VS_(L) are applied along the corresponding segment line. Thus,the segment voltage swing, i.e., the difference between the high VS_(H)and low segment voltage VS_(L), is less than the width of either thepositive or the negative stability window.

When an addressing, or actuation, voltage is applied on a common line,such as a high addressing voltage VC_(ADD) _(_) _(H) or a low addressingvoltage VC_(ADD) _(_) _(L), data can be selectively written to themodulators along that line by application of segment voltages along therespective segment lines. The segment voltages may be selected such thatactuation is dependent upon the segment voltage applied. When anaddressing voltage is applied along a common line, application of onesegment voltage will result in a pixel voltage within a stabilitywindow, causing the pixel to remain unactuated. In contrast, applicationof the other segment voltage will result in a pixel voltage beyond thestability window, resulting in actuation of the pixel. The particularsegment voltage which causes actuation can vary depending upon whichaddressing voltage is used. In some implementations, when the highaddressing voltage VC_(ADD) _(_) _(H) is applied along the common line,application of the high segment voltage VS_(H) can cause a modulator toremain in its current position, while application of the low segmentvoltage VS_(L) can cause actuation of the modulator. As a corollary, theeffect of the segment voltages can be the opposite when a low addressingvoltage VC_(ADD) _(_) _(L) is applied, with high segment voltage VS_(H)causing actuation of the modulator, and low segment voltage VS_(L)having no effect (i.e., remaining stable) on the state of the modulator.

In some implementations, hold voltages, address voltages, and segmentvoltages may be used which always produce the same polarity potentialdifference across the modulators. In some other implementations, signalscan be used which alternate the polarity of the potential difference ofthe modulators. Alternation of the polarity across the modulators (thatis, alternation of the polarity of write procedures) may reduce orinhibit charge accumulation which could occur after repeated writeoperations of a single polarity.

FIG. 5A shows an example of a diagram illustrating a frame of displaydata in the 3×3 interferometric modulator display of FIG. 2. FIG. 5Bshows an example of a timing diagram for common and segment signals thatmay be used to write the frame of display data illustrated in FIG. 5A.The signals can be applied to the, e.g., 3×3 array of FIG. 2, which willultimately result in the line time 60 e display arrangement illustratedin FIG. 5A. The actuated modulators in FIG. 5A are in a dark-state,i.e., where a substantial portion of the reflected light is outside ofthe visible spectrum so as to result in a dark appearance to, e.g., aviewer. Prior to writing the frame illustrated in FIG. 5A, the pixelscan be in any state, but the write procedure illustrated in the timingdiagram of FIG. 5B presumes that each modulator has been released andresides in an unactuated state before the first line time 60 a.

During the first line time 60 a, a release voltage 70 is applied oncommon line 1; the voltage applied on common line 2 begins at a highhold voltage 72 and moves to a release voltage 70; and a low holdvoltage 76 is applied along common line 3. Thus, the modulators (common1, segment 1), (1,2) and (1,3) along common line 1 remain in a relaxed,or unactuated, state for the duration of the first line time 60 a, themodulators (2,1), (2,2) and (2,3) along common line 2 will move to arelaxed state, and the modulators (3,1), (3,2) and (3,3) along commonline 3 will remain in their previous state. With reference to FIG. 4,the segment voltages applied along segment lines 1, 2 and 3 will have noeffect on the state of the interferometric modulators, as none of commonlines 1, 2 or 3 are being exposed to voltage levels causing actuationduring line time 60 a (i.e., VC_(REL)—relax and VC_(HOLD) _(_)_(L)—stable).

During the second line time 60 b, the voltage on common line 1 moves toa high hold voltage 72, and all modulators along common line 1 remain ina relaxed state regardless of the segment voltage applied because noaddressing, or actuation, voltage was applied on the common line 1. Themodulators along common line 2 remain in a relaxed state due to theapplication of the release voltage 70, and the modulators (3,1), (3,2)and (3,3) along common line 3 will relax when the voltage along commonline 3 moves to a release voltage 70.

During the third line time 60 c, common line 1 is addressed by applyinga high address voltage 74 on common line 1. Because a low segmentvoltage 64 is applied along segment lines 1 and 2 during the applicationof this address voltage, the pixel voltage across modulators (1,1) and(1,2) is greater than the high end of the positive stability window(i.e., the voltage differential exceeded a predefined threshold) of themodulators, and the modulators (1,1) and (1,2) are actuated. Conversely,because a high segment voltage 62 is applied along segment line 3, thepixel voltage across modulator (1,3) is less than that of modulators(1,1) and (1,2), and remains within the positive stability window of themodulator; modulator (1,3) thus remains relaxed. Also during line time60 c, the voltage along common line 2 decreases to a low hold voltage76, and the voltage along common line 3 remains at a release voltage 70,leaving the modulators along common lines 2 and 3 in a relaxed position.

During the fourth line time 60 d, the voltage on common line 1 returnsto a high hold voltage 72, leaving the modulators along common line 1 intheir respective addressed states. The voltage on common line 2 isdecreased to a low address voltage 78. Because a high segment voltage 62is applied along segment line 2, the pixel voltage across modulator(2,2) is below the lower end of the negative stability window of themodulator, causing the modulator (2,2) to actuate. Conversely, because alow segment voltage 64 is applied along segment lines 1 and 3, themodulators (2,1) and (2,3) remain in a relaxed position. The voltage oncommon line 3 increases to a high hold voltage 72, leaving themodulators along common line 3 in a relaxed state.

Finally, during the fifth line time 60 e, the voltage on common line 1remains at high hold voltage 72, and the voltage on common line 2remains at a low hold voltage 76, leaving the modulators along commonlines 1 and 2 in their respective addressed states. The voltage oncommon line 3 increases to a high address voltage 74 to address themodulators along common line 3. As a low segment voltage 64 is appliedon segment lines 2 and 3, the modulators (3,2) and (3,3) actuate, whilethe high segment voltage 62 applied along segment line 1 causesmodulator (3,1) to remain in a relaxed position. Thus, at the end of thefifth line time 60 e, the 3×3 pixel array is in the state shown in FIG.5A, and will remain in that state as long as the hold voltages areapplied along the common lines, regardless of variations in the segmentvoltage which may occur when modulators along other common lines (notshown) are being addressed.

In the timing diagram of FIG. 5B, a given write procedure (i.e., linetimes 60 a-60 e) can include the use of either high hold and addressvoltages, or low hold and address voltages. Once the write procedure hasbeen completed for a given common line (and the common voltage is set tothe hold voltage having the same polarity as the actuation voltage), thepixel voltage remains within a given stability window, and does not passthrough the relaxation window until a release voltage is applied on thatcommon line. Furthermore, as each modulator is released as part of thewrite procedure prior to addressing the modulator, the actuation time ofa modulator, rather than the release time, may determine the necessaryline time. Specifically, in implementations in which the release time ofa modulator is greater than the actuation time, the release voltage maybe applied for longer than a single line time, as depicted in FIG. 5B.In some other implementations, voltages applied along common lines orsegment lines may vary to account for variations in the actuation andrelease voltages of different modulators, such as modulators ofdifferent colors.

The details of the structure of interferometric modulators that operatein accordance with the principles set forth above may vary widely. Forexample, FIGS. 6A-6E show examples of cross-sections of varyingimplementations of interferometric modulators, including the movablereflective layer 14 and its supporting structures. FIG. 6A shows anexample of a partial cross-section of the interferometric modulatordisplay of FIG. 1, where a strip of metal material, i.e., the movablereflective layer 14 is deposited on supports 18 extending orthogonallyfrom the substrate 20. In FIG. 6B, the movable reflective layer 14 ofeach IMOD is generally square or rectangular in shape and attached tosupports at or near the corners, on tethers 32. In FIG. 6C, the movablereflective layer 14 is generally square or rectangular in shape andsuspended from a deformable layer 34, which may include a flexiblemetal. The deformable layer 34 can connect, directly or indirectly, tothe substrate 20 around the perimeter of the movable reflective layer14. These connections are herein referred to as support posts. Theimplementation shown in FIG. 6C has additional benefits deriving fromthe decoupling of the optical functions of the movable reflective layer14 from its mechanical functions, which are carried out by thedeformable layer 34. This decoupling allows the structural design andmaterials used for the reflective layer 14 and those used for thedeformable layer 34 to be optimized independently of one another.

FIG. 6D shows another example of an IMOD, where the movable reflectivelayer 14 includes a reflective sub-layer 14 a. The movable reflectivelayer 14 rests on a support structure, such as support posts 18. Thesupport posts 18 provide separation of the movable reflective layer 14from the lower stationary electrode (i.e., part of the optical stack 16in the illustrated IMOD) so that a gap 19 is formed between the movablereflective layer 14 and the optical stack 16, for example when themovable reflective layer 14 is in a relaxed position. The movablereflective layer 14 also can include a conductive layer 14 c, which maybe configured to serve as an electrode, and a support layer 14 b. Inthis example, the conductive layer 14 c is disposed on one side of thesupport layer 14 b, distal from the substrate 20, and the reflectivesub-layer 14 a is disposed on the other side of the support layer 14 b,proximal to the substrate 20. In some implementations, the reflectivesub-layer 14 a can be conductive and can be disposed between the supportlayer 14 b and the optical stack 16. The support layer 14 b can includeone or more layers of a dielectric material, for example, siliconoxynitride (SiON) or silicon dioxide (SiO₂). In some implementations,the support layer 14 b can be a stack of layers, such as, for example,an SiO₂/SiON/SiO₂ tri-layer stack. Either or both of the reflectivesub-layer 14 a and the conductive layer 14 c can include, e.g., an Alalloy with about 0.5% Cu, or another reflective metallic material.Employing conductive layers 14 a, 14 c above and below the dielectricsupport layer 14 b can balance stresses and provide enhanced conduction.In some implementations, the reflective sub-layer 14 a and theconductive layer 14 c can be formed of different materials for a varietyof design purposes, such as achieving specific stress profiles withinthe movable reflective layer 14.

As illustrated in FIG. 6D, some implementations also can include a blackmask structure 23. The black mask structure 23 can be formed inoptically inactive regions (e.g., between pixels or under posts 18) toabsorb ambient or stray light. The black mask structure 23 also canimprove the optical properties of a display device by inhibiting lightfrom being reflected from or transmitted through inactive portions ofthe display, thereby increasing the contrast ratio. Additionally, theblack mask structure 23 can be conductive and be configured to functionas an electrical bussing layer. In some implementations, the rowelectrodes can be connected to the black mask structure 23 to reduce theresistance of the connected row electrode. The black mask structure 23can be formed using a variety of methods, including deposition andpatterning techniques. The black mask structure 23 can include one ormore layers. For example, in some implementations, the black maskstructure 23 includes a molybdenum-chromium (MoCr) layer that serves asan optical absorber, an SiO₂ layer, and an aluminum alloy that serves asa reflector and a bussing layer, with a thickness in the range of about30-80 Å, 500-1000 Å, and 500-6000 Å, respectively. The one or morelayers can be patterned using a variety of techniques, includingphotolithography and dry etching, including, for example, CF₄ and/or O₂for the MoCr and SiO₂ layers and Cl₂ and/or BCl₃ for the aluminum alloylayer. In some implementations, the black mask 23 can be an etalon orinterferometric stack structure. In such interferometric stack blackmask structures 23, the conductive absorbers can be used to transmit orbus signals between lower, stationary electrodes in the optical stack 16of each row or column. In some implementations, a spacer layer 35 canserve to generally electrically isolate the absorber layer 16 a from theconductive layers in the black mask 23.

FIG. 6E shows another example of an IMOD, where the movable reflectivelayer 14 is self supporting. In contrast with FIG. 6D, theimplementation of FIG. 6E does not include support posts 18. Instead,the movable reflective layer 14 contacts the underlying optical stack 16at multiple locations, and the curvature of the movable reflective layer14 provides sufficient support that the movable reflective layer 14returns to the unactuated position of FIG. 6E when the voltage acrossthe interferometric modulator is insufficient to cause actuation. Theoptical stack 16, which may contain a plurality of several differentlayers, is shown here for clarity including an optical absorber 16 a,and a dielectric 16 b. In some implementations, the optical absorber 16a may serve both as a fixed electrode and as a partially reflectivelayer.

In implementations such as those shown in FIGS. 6A-6E, the IMODsfunction as direct-view devices, in which images are viewed from thefront side of the transparent substrate 20, i.e., the side opposite tothat upon which the modulator is arranged. In these implementations, theback portions of the device (that is, any portion of the display devicebehind the movable reflective layer 14, including, for example, thedeformable layer 34 illustrated in FIG. 6C) can be configured andoperated upon without impacting or negatively affecting the imagequality of the display device, because the reflective layer 14 opticallyshields those portions of the device. For example, in someimplementations a bus structure (not illustrated) can be included behindthe movable reflective layer 14 which provides the ability to separatethe optical properties of the modulator from the electromechanicalproperties of the modulator, such as voltage addressing and themovements that result from such addressing. Additionally, theimplementations of FIGS. 6A-6E can simplify processing, such as, e.g.,patterning.

FIG. 7 shows an example of a flow diagram illustrating a manufacturingprocess 80 for an interferometric modulator, and FIGS. 8A-8E showexamples of cross-sectional schematic illustrations of correspondingstages of such a manufacturing process 80. In some implementations, themanufacturing process 80 can be implemented to manufacture, e.g.,interferometric modulators of the general type illustrated in FIGS. 1and 6, in addition to other blocks not shown in FIG. 7. With referenceto FIGS. 1, 6 and 7, the process 80 begins at block 82 with theformation of the optical stack 16 over the substrate 20. FIG. 8Aillustrates such an optical stack 16 formed over the substrate 20. Thesubstrate 20 may be a transparent substrate such as glass or plastic, itmay be flexible or relatively stiff and unbending, and may have beensubjected to prior preparation processes, e.g., cleaning, to facilitateefficient formation of the optical stack 16. As discussed above, theoptical stack 16 can be electrically conductive, partially transparentand partially reflective and may be fabricated, for example, bydepositing one or more layers having the desired properties onto thetransparent substrate 20. In FIG. 8A, the optical stack 16 includes amultilayer structure having sub-layers 16 a and 16 b, although more orfewer sub-layers may be included in some other implementations. In someimplementations, one of the sub-layers 16 a, 16 b can be configured withboth optically absorptive and conductive properties, such as thecombined conductor/absorber sub-layer 16 a. Additionally, one or more ofthe sub-layers 16 a, 16 b can be patterned into parallel strips, and mayform row electrodes in a display device. Such patterning can beperformed by a masking and etching process or another suitable processknown in the art. In some implementations, one of the sub-layers 16 a,16 b can be an insulating or dielectric layer, such as sub-layer 16 bthat is deposited over one or more metal layers (e.g., one or morereflective and/or conductive layers). In addition, the optical stack 16can be patterned into individual and parallel strips that form the rowsof the display.

The process 80 continues at block 84 with the formation of a sacrificiallayer 25 over the optical stack 16. The sacrificial layer 25 is laterremoved (e.g., at block 90) to form the cavity 19 and thus thesacrificial layer 25 is not shown in the resulting interferometricmodulators 12 illustrated in FIG. 1. FIG. 8B illustrates a partiallyfabricated device including a sacrificial layer 25 formed over theoptical stack 16. The formation of the sacrificial layer 25 over theoptical stack 16 may include deposition of a xenon difluoride(XeF₂)-etchable material such as molybdenum (Mo) or amorphous silicon(Si), in a thickness selected to provide, after subsequent removal, agap or cavity 19 (see also FIGS. 1 and 8E) having a desired design size.Deposition of the sacrificial material may be carried out usingdeposition techniques such as physical vapor deposition (PVD, e.g.,sputtering), plasma-enhanced chemical vapor deposition (PECVD), thermalchemical vapor deposition (thermal CVD), or spin-coating.

The process 80 continues at block 86 with the formation of a supportstructure e.g., a post 18 as illustrated in FIGS. 1, 6 and 8C. Theformation of the post 18 may include patterning the sacrificial layer 25to form a support structure aperture, then depositing a material (e.g.,a polymer or an inorganic material, e.g., silicon oxide) into theaperture to form the post 18, using a deposition method such as PVD,PECVD, thermal CVD, or spin-coating. In some implementations, thesupport structure aperture formed in the sacrificial layer can extendthrough both the sacrificial layer 25 and the optical stack 16 to theunderlying substrate 20, so that the lower end of the post 18 contactsthe substrate 20 as illustrated in FIG. 6A. Alternatively, as depictedin FIG. 8C, the aperture formed in the sacrificial layer 25 can extendthrough the sacrificial layer 25, but not through the optical stack 16.For example, FIG. 8E illustrates the lower ends of the support posts 18in contact with an upper surface of the optical stack 16. The post 18,or other support structures, may be formed by depositing a layer ofsupport structure material over the sacrificial layer 25 and patterningportions of the support structure material located away from aperturesin the sacrificial layer 25. The support structures may be locatedwithin the apertures, as illustrated in FIG. 8C, but also can, at leastpartially, extend over a portion of the sacrificial layer 25. As notedabove, the patterning of the sacrificial layer 25 and/or the supportposts 18 can be performed by a patterning and etching process, but alsomay be performed by alternative etching methods.

The process 80 continues at block 88 with the formation of a movablereflective layer or membrane such as the movable reflective layer 14illustrated in FIGS. 1, 6 and 8D. The movable reflective layer 14 may beformed by employing one or more deposition processes, e.g., reflectivelayer (e.g., aluminum, aluminum alloy) deposition, along with one ormore patterning, masking, and/or etching processes. The movablereflective layer 14 can be electrically conductive, and referred to asan electrically conductive layer. In some implementations, the movablereflective layer 14 may include a plurality of sub-layers 14 a, 14 b, 14c as shown in FIG. 8D. In some implementations, one or more of thesub-layers, such as sub-layers 14 a, 14 c, may include highly reflectivesub-layers selected for their optical properties, and another sub-layer14 b may include a mechanical sub-layer selected for its mechanicalproperties. Since the sacrificial layer 25 is still present in thepartially fabricated interferometric modulator formed at block 88, themovable reflective layer 14 is typically not movable at this stage. Apartially fabricated IMOD that contains a sacrificial layer 25 may alsobe referred to herein as an “unreleased” IMOD. As described above inconnection with FIG. 1, the movable reflective layer 14 can be patternedinto individual and parallel strips that form the columns of thedisplay.

The process 80 continues at block 90 with the formation of a cavity,e.g., cavity 19 as illustrated in FIGS. 1, 6 and 8E. The cavity 19 maybe formed by exposing the sacrificial material 25 (deposited at block84) to an etchant. For example, an etchable sacrificial material such asMo or amorphous Si may be removed by dry chemical etching, e.g., byexposing the sacrificial layer 25 to a gaseous or vaporous etchant, suchas vapors derived from solid XeF₂ for a period of time that is effectiveto remove the desired amount of material, typically selectively removedrelative to the structures surrounding the cavity 19. Other combinationsof etchable sacrificial material and etching methods, e.g. wet etchingand/or plasma etching, also may be used. Since the sacrificial layer 25is removed during block 90, the movable reflective layer 14 is typicallymovable after this stage. After removal of the sacrificial material 25,the resulting fully or partially fabricated IMOD may be referred toherein as a “released” IMOD.

Description of Micromachined Piezoelectric X-Axis and Y-Axis GyroscopeImplementations

Some disclosed micromachined piezoelectric gyroscope structures providean improved mechanical sensing element that overcomes someperformance-related limitations of conventional piezoelectrictuning-fork gyroscopes.

Prior Art Gyroscopes

Conventional piezoelectric gyroscopes utilize either a single-ended or adouble-ended tuning-fork structure. FIGS. 9A and 9B show examples of thedrive and sense modes of a single-ended tuning-fork gyroscope. As shownin FIGS. 9A and 9B, single-ended tuning forks consist of two tines thatare used for both drive and sense functions. In FIGS. 9A and 9B, thedark areas indicate portions of a gyroscope 900 that are at rest and thelight areas indicate portions of the gyroscope 900 that are in motion.The tines 910 a and 910 b are piezoelectrically driven anti-phase,usually in-plane as shown in FIG. 9A. In response to an appliedrotation, Coriolis forces cause the tines 910 a and 910 b to oscillateout of plane and in opposite directions (see FIG. 9B). The resultingsense-mode oscillations generate a sense charge on piezoelectricmaterial of gyroscope 900, which may be bulk material or a piezoelectriclayer deposited on the structural material of gyroscope 900.

The primary limitation of such tuning-fork systems is that the tines 910a and 910 b that are used for sense pick-up also experience the drivemotion, which may be orders of magnitude larger than the sense motion.Thus, mechanical imperfections and asymmetries in the tines 910 a and910 b can result in a significant level of drive interference in thesense signal, which can cause quadrature and bias errors.

Another disadvantage of such tuning-fork systems is that parasiticresonant modes below operation frequencies are inevitable. In-phasetranslational modes are generally lower than anti-phase operationalmodes and can be easily excited with vibration.

In double-ended tuning-fork systems (not shown), separate tines are usedfor drive and sense functions. Two tines are driven anti-phase. TheCoriolis forces induced on the drive tines excite a common torsionalsense mode, which in turn causes vibration on the sense tines. Thedouble-ended tuning forks reduce the drive interference on the sensetines, but the efficiency for a given device size is reduced.Furthermore, many undesired parasitic modes occur below and above theoperational frequency, even more than those that occur in single-endedtuning forks.

Piezoelectric X-Axis Gyroscope Structure

The architecture of some micromachined piezoelectric gyroscopesdisclosed herein includes a proof mass that can oscillate torsionallyin-plane (about the z axis) when operating in a drive mode andtorsionally out-of-plane (about the y axis for an x-axis gyroscope andabout the x axis for a y-axis gyroscope) when operating in a sense mode.

FIG. 10A shows an example of a gyroscope 1000 having a proof masssuspended by drive beams attached to a central anchor. Here, the proofmass 1020 is suspended by flexures 1010 a and 1010 b attached to acentral anchor 1005. The drive electrodes 1015 a-d may be patterned onthe top and/or the bottom sides of the flexures. The proof mass 1020,the flexures 1010 a and 1010 b, and the central anchor 1005 can be madefrom a variety of materials such as thick, plated metal alloys (e.g.,nickel alloys such as Ni—Co, or Ni—Mn), single-crystal silicon,polycrystalline silicon, etc. In this example, the overall x and ydimensions of the gyroscope 1000 are on the order of several millimetersor less. For example, in some implementations, the width may be in therange of 0.25 mm to 1 mm and the length may be in the range of 1 mm to 4mm. The thickness may range from less than a micron to fifty microns ormore.

In this illustrated example, the drive electrodes 1015 a-d are arrangedsymmetrically on each side of a center line 1017 a. Center line 1017 acorresponds with the x axis in this example. Here, the drive electrodes1015 include piezoelectric films that are disposed on the flexures 1010a and 1010 b, allowing the flexures 1010 a and 1010 b to function asdrive beams. The piezoelectric film can be aluminum nitride (AlN), zincoxide (ZnO), lead zirconate titanate (PZT), or other thin films. In someimplementations, the drive electrodes 1015 (as well as other driveelectrodes described herein) may include a piezoelectric film disposedbetween two metal layers that are used to provide a voltage across thepiezoelectric film. The piezoelectric film may, for example, be anon-conducting piezoelectric film. Providing a voltage across the metallayers can cause movement of the drive electrodes. Alternatively, thepiezoelectric material may be single-crystal materials such as quartz,lithium niobate, lithium tantalate, etc.

In the implementation depicted in FIG. 10A, the sense electrodes 1025 aand 1025 b are piezoelectric films that are formed along the center line1017 a. In alternative implementations, the sense electrodes 1025 a and1025 b may be formed on the proof mass 1020. Alternatively, the senseelectrodes 1025 a and 1025 b may be formed on the flexures 1010 a and1010 b, on the same side as that on which the drive electrodes 1015 areformed, but in a layer either above or below the drive electrodes 1015.In some other implementations, the sense electrodes 1025 a and 1025 bmay be formed on the opposing side of the flexures 1010 a and 1010 b. Insome implementations, the sense electrodes 1025 a and 1025 b (as well asother sense electrodes described herein) may include a piezoelectricfilm disposed between two metal layers that are used to provide avoltage across the piezoelectric film. The piezoelectric film may, forexample, be a non-conducting piezoelectric film. Movement of the senseelectrodes can cause a voltage change across the metal layers.

FIG. 10B shows an example of a gyroscope implementation similar to thatof FIG. 10A, but having a gap between the drive electrodes. In thisexample, gyroscope 1000 a includes slots 1012 a and 1012 b in theflexures 1010 c and 1010 d. Here, the slots 1012 a and 1012 b aresymmetrical about the center line 1017 b. Including the slots 1012 a and1012 b may make flexures 1010 c and 1010 d relatively more compliant toin-plane forces.

When anti-phase signals are applied to the drive electrodes 1015 a-d, abending moment is generated in the flexures 1010 a-d. For example,referring to FIG. 10A, if a positive drive voltage is applied toelectrode 1015 a and a negative drive voltage is applied to electrode1015 b, one electrode will expand and the other will contract. A bendingmoment will be generated in the flexure 1010 a. Similarly, if a positivedrive voltage is applied to electrode 1015 d and a negative drivevoltage is applied to electrode 1015 c, one electrode will expand andthe other will contract, and a bending moment will be generated in theflexure 1010 b. When the flexures 1010 a and 1010 b are actuated inopposite directions, a torsional in-plane drive mode is excited. Thesense electrodes 1025 a and 1025 b detect out-of-plane torsionalmovement of the proof mass 1020 in response to an applied rotation aboutthe x axis. Similarly, the sense electrodes 1025 c and 1025 d disposedon the proof mass 1020 of FIG. 10B may be used to detect applied angularrotation about the x axis.

In FIGS. 11A and 11B, the darkest areas indicate portions of thegyroscope 1000 that are substantially at rest and the light areasindicate portions of the gyroscope 1000 that are in motion. FIG. 11Ashows an example of a drive mode of an implementation such as that shownin FIG. 10A. In FIG. 11A, the side 1105 a of the gyroscope 1000 isdriven in the direction indicated by arrow 1110 a while the side 1105 bof the gyroscope 1000 is driven in the direction indicated by arrow 1110b. When the polarities of the drive voltages are reversed, the sides1105 a and 1105 b are driven in directions opposite to that shown. Inthis manner, the proof mass 1020 may be driven in an oscillatorytorsional mode at a frequency nominally equal to the frequency of thedrive voltages.

FIG. 11B shows an example of a sense mode of an implementation beingdriven as shown in FIG. 11A. In the presence of an applied rotationabout the x axis, a net Coriolis moment about the y-axis may be inducedon the proof mass 1020. As shown in FIG. 11B, the Coriolis momentexcites the out-of-plane sense mode, which bends the sides 1105 a and1105 b out-of-plane in opposite directions. This sense motion cangenerate a piezoelectric charge on the sense electrodes 1025 a-d asdepicted in FIGS. 10A and 10B.

Implementations such as those depicted in FIGS. 10A and 10B cansubstantially eliminate the in-phase modes that are inherent in aconventional tuning-fork system. Some such implementations may furtherenhance performance by utilizing a large proof mass 1020.

Drive and Sense Decoupling

In the simple implementations described above, the sense electrodes 1025a-d may be subject to the drive motion. Even though the effects of thedrive motion may be common-mode rejected, asymmetries and imperfectionsmay cause coupling of the drive motion into the sense signal path. Insome high performance applications, the resulting errors could causeless-than-optimal performance.

In order to reduce the drive interference when sensing, the drive andsense beams can be separated by utilizing a frame structure. Two generalapproaches for decoupling the drive and sense modes are described below.The gyroscopes described below may have overall lengths and widths thatare on the order of several millimeters or less. For example, someimplementations have lengths in the range of 0.5 mm to 3 mm and widthsin the range of 0.3 mm to 1.5 mm, with thicknesses between about one andfifty microns or more.

Drive Frame Implementations

Some drive frame gyroscope implementations include a drive frame thatoscillates only in the drive mode. The drive frame may be disposedbetween a central anchor and a proof mass. Such implementations may moreeffectively decouple the drive motion from the sense motion, as comparedto the implementations shown in FIGS. 10A and 10B.

FIG. 12 shows an example of a drive frame gyroscope implementation inwhich a drive frame is attached to a central anchor via drive beams:here, a drive frame 1210 of the gyroscope 1200 surrounds a centralanchor 1205 and is attached to the central anchor 1205 via the drivebeams 1215 a-d. In this example, slots 1207 separate the drive frame1210 from most of the central anchor 1205.

A proof mass 1220 surrounds the drive frame 1210. The proof mass 1220 iscoupled to the drive frame 1210 by the sense beams 1225 a-d. In thisexample, the proof mass 1220 is only coupled to the drive frame 1210 atdistal ends 1226 of the sense beams 1225 a-d, away from a central axis1218, which corresponds with the y axis in this example. The slots 1217and 1229 separate other portions of the sense beams 1225 a-d from theproof mass 1220. Slots 1217 also separate the drive frame 1210 from theproof mass 1220.

Drive beams 1215 a-d are disposed symmetrically about a center line1231, which corresponds with the x axis in this example. To generatedrive oscillations, a differential drive can be used. In suchimplementations, two drive beams on one side of the anchor 1205 may beactuated with anti-phase signals in one direction, and another two beamson the other side of the anchor 1205 may be actuated in the oppositedirection to generate a net rotation about the z axis. Here, a negativevoltage is applied to drive electrodes (not shown) of the drive beams1215 a and 1215 d at the same time that a positive voltage is applied todrive electrodes of the drive beams 1215 b and 1215 c.

In this example, the drive and sense electrodes include piezoelectricfilms that may be seen more clearly in FIGS. 13A and 13B. FIG. 13A showsan example of a cross-section of a gyroscope implementation such as thatshown in FIG. 12. In this view of the gyroscope 1200, the piezoelectricsense electrode 1305 a of the sense beam 1225 a and the piezoelectricsense electrode 1305 b of the sense beam 1225 b may clearly be seen. Thepiezoelectric sense electrodes 1305 c and 1305 d of the sense beams 1225c and 1225 d, respectively, may also be seen. FIG. 13B shows an exampleof an enlarged pair of drive beams of the gyroscope implementation shownin FIG. 13A. In FIG. 13B, the piezoelectric drive electrodes 1305 e and1305 f may be seen on the drive beams 1215 a and 1215 b, respectively.As discussed in detail below with reference to FIG. 41 et seq., in someimplementations a single layer may be deposited and patterned to formthe piezoelectric film of the electrodes 1305 a-f.

Although the piezoelectric drive and sense electrodes described hereinare often illustrated on top of gyroscope drive and sense frames, proofmasses, etc., such illustrations are primarily made for the purpose ofclarity. In alternative implementations, such drive and sense electrodesmay be positioned “underneath” (closer to the substrate than) the driveand sense frames, proof masses, etc. As described below with referenceto FIGS. 41 through 46B, it can be advantageous to form the drive andsense electrodes before forming the drive frames, sense frames, proofmasses, etc. Such fabrication methods may produce gyroscopes wherein thedrive and sense electrodes are disposed underneath the drive frames,sense frames, proof masses, etc.

FIG. 14A shows an example of a drive mode of a gyroscope implementationsuch as that shown in FIG. 12. In FIGS. 14A and 14B, the cool-coloredportions of the gyroscope 1200 are moving relatively less than thehot-colored portions: the blue portions of the gyroscope 1200 aresubstantially at rest, whereas the red- and orange-colored portions aremoving more than the other portions of the gyroscope 1200. Here, thedrive beams 1215 are being driven via a differential piezoelectricdrive, as described above.

The drive beams 1215 are relatively compliant to in-plane motion, whichallows the gyroscope 1200 to rotate about the z axis. The drive beams1215 may be made relatively stiff in all other directions, thussubstantially constraining the drive frame to rotate only in the drivemode (i.e., the x-y plane). Here, for example, the drive beams 1215 arerelatively stiff along the x axis, in order to suppress undesirablemodes of oscillation. For example, the portions of slots 1207 thatparallel center line 1218 create perforations along the y axis of thedrive frame 1210. Without the extra stiffness, those perforations wouldtend to form a compliant hinge along the y axis, allowing the driveframe 1210 to bend around the hinge.

FIG. 14B shows an example of a sense mode of a gyroscope implementationbeing driven as shown in FIG. 14A. In the sense mode, the proof mass1220 oscillates about the y axis, which induces a stress on the sensebeams 1225 a-d. Here, the proof mass side 1220 a is moving upwards atthe same time that the proof mass side 1220 b is moving downwards. Thisout-of-plane sense motion causes the sense beams 1225 a-d to bendout-of-plane and causes a piezoelectric charge to be generated by thecorresponding sense electrodes 1305 a-d. At the moment depicted in theexample of FIG. 14B, the sense beams 1225 c and 1225 d bend downwards,while the sense beams 1225 a and 1225 b bend upwards. Thus, the topsurface of the sense beams 1225 c and 1225 d expands, and the topsurface of the sense beams 1225 a and 1225 b contracts. When the drivemotion is in the opposite direction, the sense beams 1225 c and 1225 dbend upwards, while the sense beams 1225 a and 1225 b bend downwards.Such implementations can provide a differential detection mechanism,wherein the sensor output is the sum of the electrodes of the sensebeams 1225 a and 1225 b minus the sum of the electrodes of the sensebeams 1225 c and 1225 d, or vice versa, depending on the orientation.

In this configuration of the gyroscope 1200, the sense motions of theproof mass 1220 are substantially decoupled from the drive frame 1210.Decoupling the drive and sense motions helps to keep the senseelectrodes quieter, in part because the sense electrodes do not undergothe large-amplitude drive motions. In some such implementations, thesense beams may be only axially loaded due to the drive motion.

In the configurations depicted in FIGS. 12 through 14B, the sense beams1225 a-d are substantially rectangular in the x-y plane. However, inalternative implementations, the sense beams 1225 a-d have other shapes.In some such implementations, the sense beams 1225 a-d are tapered,e.g., as shown in FIG. 17.

Sense Frame Implementations

Various sense frame gyroscope implementations described herein include asense frame that oscillates in the sense mode, but is substantiallystationary in the drive mode. FIG. 15 shows an example of a sense framegyroscope implementation. The sense frame 1510 may be connected to theproof mass 1530 via drive beams 1515 a-d. Here, the drive beams 1515 a-dconnect a central portion 1510 a of the sense frame 1510 to the proofmass 1530. Central portion 1510 a is disposed between a pair of anchors1505 a and 1505 b. Here, the anchors 1505 a and 1505 b are separatedfrom the central portion 1510 a by slots 1522.

The gyroscope 1500 features a sense frame 1510 that is connected to theanchors 1505 a and 1505 b via the sense beams 1520 a-d. In this example,the sense frame 1510 includes tapering portions 1512, each of which arewider at a first end 1513 near one of the anchors 1505 a or 1505 b andnarrower at a second end 1514 away from the anchors 1505 a or 1505 b.Each of the sense beams 1520 a-d extends from one of the anchors 1505 aor 1505 b to one of the second ends 1514. Here, the sense beams 1520 a-dare only connected to the sense frame 1510 at the second ends 1514. Thesense beams 1520 a-d are separated from the first ends 1513 by slots1522.

The proof mass 1530 is separated from the sense beams 1520 and from thesense frame 1510 by the slots 1524. Moreover, the proof mass 1530 isseparated from the sense frame 1510 by the slots 1517. Accordingly, thesense frame 1510 is substantially decoupled from the drive motions ofthe proof mass 1530.

FIG. 16A shows an example of a drive mode of the gyroscopeimplementation shown in FIG. 15. In FIG. 16A, the displacement of theproof mass 1530 with respect to the sense frame 1510 is exaggerated inorder to see their relative motions more clearly. The dark blue portionsof the gyroscope 1500 are substantially at rest, whereas the red- andorange-colored portions are moving more than the other portions of thegyroscope 1500. Here, the sense frame 1510 is shown in a uniformly darkblue shade, indicating that the sense frame 1510 is not substantially inmotion. The displacement of the proof mass 1530 increases withincreasing distance from the anchors 1505, as indicated by the colorprogression from light blue to red.

The sense frame 1510 is coupled to the proof mass 1530 not only by thedrive beams 1515, but also by the linkage beams 1525. The drive beams1515 and the linkage beams 1525 are compliant to in-plane deformationand allow the proof mass 1530 to rotate in-plane in the drive mode withrespect to the sense frame. However, the sense frame 1510 issubstantially decoupled from the drive motions of the proof mass 1530.

FIG. 16B shows an example of a sense mode of the gyroscopeimplementation being driven as shown in FIG. 16A. During sense modeoperations, the proof mass 1530 and the sense frame 1510 can oscillatetogether torsionally out-of-plane. At the moment depicted in FIG. 16B,an end 1605 of the proof mass 1530 is bending upwards and an end 1610 ofthe proof mass 1530 is bending downward. Here, the linkage beams 1525are stiff with regard to out-of-plane forces. Therefore, the linkagebeams 1525 increase the transfer of the sense motions of the proof mass1530 to the sense frame 1510.

Tapered Sense Beams

The electrical sensitivity of the piezoelectric gyroscope system can beincreased by improving the stress uniformity on the sense beams. Forsome implementations of a rectangular sense beam, the maximum bendingstress on the sensing beam is at the anchor connection and reduceslinearly with the distance from the anchor. This configuration canresult in reduced total piezoelectric charge at the sense electrode.

By using a tapered sense beam profile, the reduction in bending stresscan be compensated by the stress increase due to a gradually reducingbeam width. Thus, a uniform stress profile may be achieved along thesense beam, and the charge generated throughout the sense electrode maybe maximized.

FIG. 17 shows an example of an alternative sense frame gyroscopeimplementation having tapered sense beams. Many features of thegyroscope 1700 are similar to corresponding features of the gyroscope1500. For example, the drive beams 1715 connect a central portion of thesense frame 1710 to the proof mass 1730. The sense beams 1720 a-d extendfrom the anchors 1705 a and 1705 b to the distal ends 1714 of the senseframe 1710, away from the anchors 1705 a and 1705 b.

The proof mass 1730 is separated from the sense beams 1720 a-d by theslots 1724. Moreover, the proof mass 1730 is separated from most of thesense frame 1710 by the slots 1717. Like the sense frame 1510 of thegyroscope 1500, the sense frame 1710 is substantially decoupled from thedrive motions of the proof mass 1730.

In the example shown in FIG. 17, however, a tapered sense beam design isincorporated into the decoupled sense-frame implementation. In thegyroscope 1700, the sense beams 1720 a-d have widths that decrease withincreasing distance from the anchors 1705 a and 1705 b. For example,tapered sense beam 1720 c includes a wider end 1722 that is attached tothe anchor 1705 b and a narrower end 1723 that is attached to the senseframe 1710.

When the stresses on the sense beams during the sense motion are modeledaccording to a finite element analysis (FEA), it may be observed thatsome implementations of the tapered sense beam design provide moreuniform stresses along the sense beam. FIG. 18 shows an example of afinite element analysis superimposed upon a gyroscope implementationsuch as that of FIG. 17, showing substantially uniform stresses on thetapered sense beams when operating in a sense mode. The substantiallyuniform light shading on tapered sense beams 1720 a and 1720 c indicatessubstantially uniform compression, whereas the substantially uniformdark shading on tapered sense beams 1720 b and 1720 d indicatessubstantially uniform tension.

FIG. 19 shows an example of a plot of the stress level on the taperedsense beams versus the distance from the center (y axis) for a gyroscopeimplementation such as that of FIG. 17. In FIG. 19, the stresses alongthe sense beams 1720 c and 1720 d are plotted with respect to distancealong the x axis. It may be observed from FIG. 19 that the stress levelin this implementation remains relatively constant and does notsubstantially reduce with position along each sense beam. Region 1905corresponds with the substantially uniform tension of the tapered sensebeam 1720 d, whereas region 1910 corresponds with the substantiallyuniform compression of the tapered sense beam 1720 c. With an optimaltaper angle, a substantially constant stress level across each sensebeam 1720 a-d can be achieved. The optimal taper angle will varyaccording to the gyroscope design and may be determined by repeated FEAmodeling. The optimal taper angle will correspond to the “flattest” orleast varying curve in areas 1905 and 1910.

Although tapered sense beams have been shown herein in the context ofsense frame gyroscope implementations, tapered sense beams also can beused to improve sensitivity in other implementations. For example,tapered sense beams can be used in drive frame gyroscope implementationssuch as those described above with reference to, e.g., FIG. 15.

Aside from the tapered sense beams 1720, there are some additionaldifferences between the gyroscope 1500 and the gyroscope 1700. Referringagain to FIG. 17, it may be observed that the linkage beams 1725 areserpentine flexures and are connected to distal portions of the senseframe 1710, relatively farther from the y axis than in the gyroscope1500. This is a slight improvement over the configuration of thegyroscope 1500 in terms of coupling the sense motion of the proof mass1730, because forces are being applied farther away from y axis, nearerto the point of maximum amplitude of the sense motion of the proof mass1730. Moving the applied force closer to the tip of the wing-shapedsense frame 1710 imparts relatively more force from the proof mass 1730to the sense frame 1710.

Moreover, in the gyroscope 1700, portions of the slots 1726 (whichseparate the anchors 1705 a and 1705 b from the sense frame 1710) aresubstantially parallel to corresponding portions of the slots 1717(which separate the sense frame 1710 from the proof mass 1730). Thismodification can help to provide sufficient stiffness in thecorresponding portions of the sense frame 1710.

Description of Micromachined Piezoelectric Z-Axis GyroscopeImplementations

Some implementations described herein provide a z-axis gyroscope withlow quadrature and bias errors. Some implementations include a driveproof mass that is piezoelectrically driven in a substantially linear,x-directed motion (in-plane). The drive proof mass may be mechanicallycoupled to a sense proof mass, which vibrates torsionally in thepresence of an angular rotation about the z axis. Motion of the senseproof mass can induce charge in a piezoelectric film disposed above orbelow sense beams that connect the sense mass to the substrate anchor.The induced charge can cause a change in voltage of piezoelectric senseelectrodes, which may be recorded and processed electronically.

The proof masses can be made from a variety of materials such as thick,plated metal alloys (e.g., nickel alloys such as Ni—Co, Ni—Mn, etc.),single crystal silicon from the device layer of an SOI wafer, glass, andothers. The piezoelectric film can be aluminum nitride (AlN), zinc oxide(ZnO), lead zirconate titanate (PZT), or other thin films, or singlecrystal materials such as quartz, lithium niobate, lithium tantalate,and others. Some implementations are well suited for manufacturing onflat-panel display glass.

Some implementations also involve the use of an array of electrostaticactuators to tune the mechanical mode shape of the drive motion in orderto suppress coupling of quadrature into the sense frame. For example, insome implementations, the electrostatic actuators include an array ofcomb-finger electrodes to fine-tune an in-plane motion of the proof massand/or an electrostatic gap between the substrate and proof mass tosuppress undesired vertical motion, as described more fully below withreference to FIG. 23.

Z-Axis Gyroscope Architecture

FIG. 20A shows an example of a plan view of a z-axis gyroscope 2000implementation. The gyroscope 2000 includes a sense frame 2010 disposedaround a central anchor 2005. The sense frame 2010 is connected to thecentral anchor 2005 via the sense beams 2020 a-d.

A drive frame 2030 is disposed around and connected to the sense frame2010. In this example, the drive beams 2015 a-d piezoelectrically drivethe drive frame 2030 in a substantially linear, x-directed motion(in-plane). Here, the drive frame 2030 is composed of the drive frameportions 2030 a and 2030 b. The drive frame 2030 can be actuated byapplying anti-phase voltages to each pair of adjacent drive beams, e.g.,a positive voltage to the drive beam 2015 a and a negative voltage tothe drive beam 2015 b.

FIG. 20B shows an example of an enlarged view of the drive beams 2015 cand 2015 d of the z-axis gyroscope implementation shown in FIG. 20A. Inthis enlarged view, the drive beams 2015 c and 2015 d may be seen moreclearly. The drive beams 2015 c and 2015 d are joined to the drive frameportion 2030 b by flexure 2045 b, which is disposed within slot 2035 c.The electrodes 2050 a and 2050 b (each of which includes a piezoelectricfilm) are disposed on the drive beams 2015 c and 2015 d, respectively.In this example, a positive voltage is being applied to the electrode2050 b at the same time that a negative voltage is being applied to theelectrode 2050 a. The applied voltages cause compressional stress to beapplied to the drive beam 2015 d and a tensional stress to be applied tothe drive beam 2015 c. The opposing axial strains induced by thepiezoelectric material cause a net moment that moves the drive frameportion 2030 b in a positive x direction.

FIG. 21A shows an example of a drive mode of a z-axis gyroscopeimplementation such as that depicted in FIG. 20A. In FIGS. 21A and 21B,the displacements are exaggerated to facilitate ease of viewing. In FIG.21A, the drive frame portion 2030 b has moved in a positive x directionand the drive frame portion 2030 a has moved in a negative x direction.However, the drive motion is substantially decoupled from the senseframe 2010. Therefore, the sense frame 2010 does not translate along thex axis. Instead, the sense frame 2010 remains substantially stationaryin the absence of rotation about the z axis.

The functionality of the gaps 2035 a-e and the flexures disposed thereinare apparent in FIG. 21A. The gaps 2035 a-e are substantially parallelto the y axis. The gap 2035 b, which extends substantially along the yaxis, has opened. Flexures 2047 a and 2047 b, which span the gap 2035 band which connect the drive frame portions 2030 a and 2030 b, also haveopened. The flexures 2040 a and 2040 b, which extend along the gaps 2035d and 2035 e, are compliant to in-plane bending and allow the senseframe 2030 to remain in substantially the same position when the driveframe portions 2030 a and 2030 b are driven. Similarly, the flexures2045 a and 2045 b, which extend along the gaps 2035 a and 2035 b, alsoallow the sense frame 2010 to remain in substantially the same positionwhen the drive frame 2030 is driven.

FIG. 21B shows an example of a sense mode of a z-axis gyroscopeimplementation driven as depicted in FIG. 21A. The sense beams 2020 arecompliant to rotation around the z axis. Accordingly, the sense frame2010 can vibrate torsionally in the presence of an angular rotation.These torsional sense motions of the sense frame 2010 can induce strainand charge in piezoelectric films disposed on the sense beams 2020. Itmay be observed from FIG. 21B that flexures 2047 a and 2047 b also canbe deformed by the sense motion of the sense frame 2010. However,flexures 2040 a, 2040 b, 2045 a and 2045 b are not substantiallydeformed.

In the z-axis gyroscope implementations disclosed herein, the drive andsense frames may be designed with mechanically orthogonal modes ofvibration. As shown in FIG. 21A, in some implementations, the drivesuspension can restrict the drive motion to that of a substantiallylinear displacement along the x-axis.

In contrast, the sense frame suspension may be compliant to torsionalrotations about the z axis, but may be comparatively stiff totranslational motion in the x or y directions. The flexures connectingthe drive frame 2030 and the sense frame 2010 may be made compliant tox-directed (quadrature) forces, but comparatively stiff to they-directed, Coriolis-coupled torsional forces. Such configurations maysubstantially reduce drive motion quadrature coupling from the drivemotion to the sense motion.

Moreover, in some implementations the elements of the gyroscopedifferential drive frame may be mechanically coupled to reduce thenumber of parasitic resonances and to separate frequencies of thesymmetric and anti-symmetric modes. Consequently, these implementationsresist quadrature-induced parasitic resonances.

Sense Beam Optimization

The electrical sensitivity of the piezoelectric gyroscope system can beincreased by improving the stress uniformity on the sense beams. For asense beam with a uniform rectangular cross-section, the bending stresson the sensing beam is a maximum at the anchor connection and reduceslinearly as a function of the distance from the anchor. This results ina less-than-optimal integrated piezoelectric charge, and consequentlyvoltage, on the sense electrode.

FIG. 22 shows an example of a close-up view of one implementation of atapered sense beam from a z-axis gyroscope. As shown in FIG. 22, byutilizing a tapered sense beam profile, a substantially uniform stressprofile may be achieved along the sense beams 2020 c and 2020 d.Accordingly, the total charge generated on the sense electrode may beenhanced.

Fabrication on Flat-Panel Display Glass

Some x-axis, y-axis and z-axis gyroscopes disclosed herein are wellsuited to manufacturing on large-area flat panel display glass. In someimplementations using plated metal alloy proof masses and a sputteredpiezoelectric AlN film, processing could occur at less than 400° C. Aplated metal proof mass can have high mass density (as compared tosilicon), and the absence of deep reactive-ion etching (DRIE) sidewallslope, which is common to silicon-based electrostatic designs andinduces quadrature. Details of some fabrication processes are describedbelow with reference to FIG. 41 et seq.

In some implementations, glass may serve as both the substrate and thepackage, resulting in a reduction in component cost. A z-axis gyroscopecan be integrated with a number of other sensors and actuators, such asaccelerometers, x-axis and/or y-axis gyroscopes, magnetometers,microphones, pressure sensors, resonators, actuators and/or otherdevices.

Quadrature Tuning with Electrostatic Actuators

Some implementations described herein involve the use of an array ofelectrostatic actuators to actively fine-tune the mechanical mode shapeof the drive and/or sense frames in order to suppress quadrature andbias errors. Quadrature can be caused by unwanted deflections in thedrive frame coupling to the sense frame.

FIG. 23 shows an example of an electrode array that may be configured toapply corrective electrostatic forces to fine-tune the vibrational modeshapes of a proof mass. FIG. 23 depicts a proof mass 2305, which may bea gyroscope or an accelerometer proof mass. The desired motion of theproof mass 2305 is in-plane, as shown. However, the vibrational modes ofthe proof mass 2305 may have out-of-plane components. One example ofsuch an out-of-plane component, a small, vertical, undesired deflection(shown as the dashed outline of the proof mass 2305), is shown in FIG.23 as being superimposed on the primary in-plane translation drive mode.The electrode array 2310 can be configured for applying an electrostaticcorrecting force to the proof mass 2305. By controlling the electrodearray 2310 to actively apply an electrostatic force that cancels theundesired vertical component of motion of the proof mass 2305,quadrature-inducing accelerations that couple to the sense frame can bereduced.

The concept can be applied to a number of other implementations as well.For example, the electrostatic actuators may be composed of comb fingersconfigured to apply an electrostatic force for canceling out anundesired y-directed motion.

Description of Accelerometer Implementations

Various implementations described herein provide novel three-axisaccelerometers, as well as components thereof. Such three-axisaccelerometers have sizes, performance levels and costs that aresuitable for use in a wide variety of consumer electronic applications,such as portable navigation devices and smart phones. Some suchimplementations provide a capacitive stacked lateral overlap transducer(SLOT) based three-axis accelerometer. Some implementations providethree-axis sensing using two proof masses, whereas other implementationsprovide three-axis sensing using only one proof mass. Different flexuretypes may be optimized for each axis.

Implementations of the accelerometer may be fabricated on large-areasubstrates, such as large-area glass panels. As described in detailbelow, the fabrication processes used in forming SLOT-based three-axisaccelerometers on large-area substrates can be compatible with processesfor fabricating gyroscopes on large-area substrates. Combining suchprocesses can enable the monolithic integration of six inertial sensingaxes on a single glass substrate.

For x-y axis in-plane sensing, some implementations provide a conductiveproof mass and patterned electrodes on either side of a sacrificial gap.In-plane applied acceleration translates the proof mass laterally, whichdecreases the overlap between the first electrode and the proof mass andincreases the overlap between the second electrode and the proof mass.In-plane bending flexures may provide structural support for a suspendedproof mass.

For z-axis out-of-plane sensing, moment imbalances on either side of apivot may be created by making one side of the proof mass relativelymore (or less) massive than the other side of the proof mass. Forexample, moment imbalances on either side of the pivot may be created byperforating one side of the proof mass and/or by forming the proof masswith a different width and/or length on either side. In someimplementations, a negative z-acceleration rotates the proof massclockwise, which increases the gap between the first electrode and theproof mass and decreases the gap between the second electrode and theproof mass. The z-axis accelerometer may include torsional flexures. Insome implementations, three-axis sensing can be achieved using one ortwo proof masses. Some examples are described below.

FIG. 24 shows an example of an accelerometer for measuring in-planeacceleration. The accelerometer 2400 includes electrodes 2405 a and 2405b formed on the substrate 2401. The electrodes 2405 a and 2405 b may beformed from any convenient conducting material, such as metal. Theaccelerometer 2400 includes a conductive proof mass 2410 that isseparated from the electrodes 2405 a and 2405 b by a gap 2415. The gap2415 may, for example, by on the order of microns, e.g., 0.5 or 2microns, or can be considerably smaller or larger.

The conductive proof mass 2410 includes a slot 2420. In this example,the edges 2425 of the slot 2420 are suspended over the electrodes 2405 aand 2405 b when the accelerometer 2400 is at rest. The slot 2420 mayextend partially or completely through the conductive proof mass 2410,depending on the implementation. The capacitance of various conductiveproof masses 2410 having different slot depths is shown in FIG. 32,which is described below. Accelerometers having the generalconfiguration of the accelerometer 2400 may be referred to herein asstacked lateral overlap transducer (SLOT)-based accelerometers.

A positive x-acceleration translates the conductive proof mass 2410laterally, which shifts the position of the slot 2420. More of the slot2420 is positioned over the electrode 2405 a, which causes more air andless conductive material to be positioned near the electrode 2405 a.This decreases the capacitance at the electrode 2405 a by AC.Conversely, less of the slot 2420 is positioned over the electrode 2405b, which causes less air and more conductive material to be positionednear the electrode 2405 b. This increases the capacitance at theelectrode 2405 b by ΔC. A corresponding in-plane accelerationdifferential output signal that is proportional to 2ΔC results from thechange in overlap caused by the translation of the conductive proof mass2410.

FIG. 25 shows an example of an accelerometer for measuring out-of-planeacceleration. In this example, the accelerometer 2500 includes aconductive proof mass 2510 that is attached to a substrate 2401 by asupport 2515 and a torsional flexure 2525. The support 2515 and thetorsional flexure 2525 form a pivot 2530. A moment imbalance can becreated on either side of the support 2515, e.g., by perforating oneside of the conductive proof mass 2510, by making the conductive proofmass 2510 a different width and/or length on either side the support2515, or by combinations thereof. A moment imbalance also may be createdby making one side of the conductive proof mass 2510 from material thatis relatively more or less dense than the material used to form theother side of the conductive proof mass 2510. However, suchimplementations may be relatively more complex to fabricate. In thisexample, a moment imbalance has been created by making perforations 2520in the side 2510 b.

A negative z-acceleration rotates the conductive proof mass 2510clockwise, which increases a gap between the electrode 2405 c and theconductive proof mass 2510 and decreases a gap between the electrode2405 d and the conductive proof mass 2510. This decreases thecapacitance at the electrode 2405 c by ΔC and increases the capacitanceat the electrode 2405 d by ΔC. A corresponding out-of-plane accelerationoutput signal proportional to 2ΔC results.

FIG. 26A shows an example of an accelerometer for measuring in-planeacceleration. The accelerometer 2400 a may have overall x and ydimensions on the order of a few millimeters. In some implementations,the accelerometer 2400 a may have x and y dimensions of less than amillimeter.

In this example, the accelerometer 2400 a includes a conductive proofmass 2410 a disposed around an inner frame 2610 a. The conductive proofmass 2410 a includes slots 2420 a that extend substantially along afirst axis, which is the x axis in this example. The conductive proofmass 2410 a also includes slots 2420 b that extend substantially along asecond axis, which is the y axis in this example. As described in moredetail below, the conductive proof mass 2410 a is constrained to movesubstantially along the x axis, the y axis, or a combination of the xand y axes.

The inner frame 2610 a includes a substantially stationary portion 2612a, which is connected to a substrate via an anchor 2605. The anchor 2605is disposed underneath the plane depicted in FIG. 26A. Here, thestationary portion 2612 a also includes a pair of stress isolation slits2625, which extend substantially along the y axis in this example. Thestress isolation slits 2625 can desensitize acceleration measurements tostresses in the film, substrate and/or package. The inner frame 2610 aalso includes a movable portion 2614 a. The flexures 2615 a connect themovable portion 2614 a to the conductive proof mass 2410 a. The flexures2620 a connect the movable portion 2614 a to the stationary portion 2612a. The flexures can be folded flexures, which can increase bendingcompliance. In some embodiments, the flexures may be serpentineflexures. In this example, the inner frame 2610 a includes a pluralityof slots 2420 a. Additional slots 2420 a may be formed in proof mass2410 a, as shown in FIG. 26A.

FIG. 26B shows an example of the response of the accelerometer of FIG.26A to acceleration along a first axis. Here, the conductive proof mass2410 a of the accelerometer 2400 a is moving along the x axis. The slots2420 b are shifted along the x axis, which causes a change incapacitance to be detected by the corresponding electrodes 2405, asdescribed above with reference to FIG. 24. The electrodes 2405 aredisposed on a substrate 2401 (not shown) underlying the planeillustrated in FIG. 26B. The special relationships between accelerometer2400 a, the substrate 2401 and the electrodes 2405 are illustrated inFIG. 28 and are described below. The flexures 2615 a, which are deformedin FIG. 26B, allow the conductive proof mass 2410 a to move along the xaxis while the inner frame 2610 a remains substantially stationary. Inthis implementation, the flexures 2620 a are not substantially deformed.The capacitance associated with slots 2420 a is substantially unchangedunder x translation of the proof mass.

FIG. 26C shows an example of the response of the accelerometer of FIG.26A to acceleration along a second axis. Here, the conductive proof mass2410 a and the movable portion 2614 a of the inner frame 2610 a aremoving along the y axis. The slots 2420 a are shifted along the y axis,which causes a change in capacitance to be detected by the correspondingelectrodes 2405, as described above. The flexures 2620 a, which aredeformed in FIG. 26C, allow the movable portion 2614 a to move along they axis with the conductive proof mass 2410 a. In this implementation,the flexures 2615 a are not substantially deformed. The capacitanceassociated with the slots 2420 b is substantially unchanged under ytranslation of the proof mass 2410 a and the movable portion 2614 a.

FIG. 26D shows an example of an accelerometer for measuring in-plane andout-of-plane acceleration. In this example, the accelerometer 2400 bincludes a conductive proof mass 2410 b having an extension 2670. Theextension 2670 causes the portion of conductive proof mass 2410 b thatis on the side of the extension 2670 to be more massive than the portionof conductive proof mass 2410 b that is on the other side of the anchor2605. The extra mass of the extension 2670 creates a moment imbalance ofthe type described above with reference to FIG. 25, allowing theaccelerometer 2400 b to be sensitive to acceleration along the z axis.

There are other differences between the accelerometer 2400 b and theaccelerometer 2400 a described in the previous drawings. In theimplementation depicted in FIG. 26D, the stationary portion 2612 b ofthe inner frame 2610 b is relatively smaller than the stationary portion2612 a of the inner frame 2610 a in the implementation depicted in,e.g., FIG. 26A. This configuration allows the slots 2420 a to occupyrelatively more area of the inner frame 2610 b, which can result ingreater sensitivity for measuring acceleration along the y axis.Moreover, in the implementation depicted in FIG. 26D, the flexures 2615b and 2620 b are serpentine flexures.

FIG. 27 shows an example of an accelerometer for measuring out-of-planeacceleration. The z-axis accelerometer 2500 a is configured to operateaccording to the general principles of the accelerometer 2500, describedabove with reference to FIG. 25. Here, the conductive proof mass 2510 isattached to a substrate 2401 (not shown) by an anchor 2515 a and a pairof torsional flexures 2525 a that form a pivot 2530 a. A momentimbalance has been created on either side of the pivot 2530 a by makingthe side 2510 b of the conductive proof mass 2510 relatively smallerthan the other side 2510 a.

The electrodes 2405 c and 2405 d are disposed in a plane below theaccelerometer 2500 a on the substrate 2401, as shown in FIGS. 25 and 28.In this example, the electrode 2405 c is inset from an edge of the side2510 b of the conductive proof mass 2510 by a distance 2710. Anacceleration along the z axis causes the conductive proof mass 2510 torotate about the y axis and about the pivot 2530 a, as described abovewith reference to FIG. 25. For example, an acceleration along the z axisrotates the side 2510 a of the conductive proof mass 2510 in a negativez direction (towards the electrode 2405 d) and rotates the side 2510 bin a positive z direction (away from the electrode 2405 c). Thisrotation of the conductive proof mass 2510 about the pivot 2530 adecreases the capacitance at the electrode 2405 c by ΔC and increasesthe capacitance at the electrode 2405 d by ΔC, as described above withreference to FIG. 25. A corresponding out-of-plane acceleration outputsignal proportional to 2ΔC results. The change in capacitance at theelectrodes 2405 c and 2405 d may depend on various factors, such as thesize of the electrodes 2405 c and 2405 d, the magnitude of theacceleration along the z axis, etc. In some implementations, the changein capacitance at the electrodes 2405 c and 2405 d may be in the rangeof femtofarads.

FIG. 28 shows an example of an alternative accelerometer implementationfor measuring in-plane and out-of-plane acceleration. In this example, athree-axis accelerometer 2800 combines the z-axis accelerometer 2500 a(FIG. 27) with the x-y axis accelerometer 2400 a (FIGS. 26A-C). In someimplementations, the accelerometer 2800 may have a length 2805 and awidth 2810 that are on the order of a few millimeters or less. Forexample, the length 2805 may be in the range of 0.5 to 5 mm, whereas thewidth may be in the range of 0.25 to 3 mm.

The electrodes 2405 c-f are disposed on areas of the substrate 2401 nextto which the accelerometer 2500 a and the accelerometer 2600 a will befabricated. The electrodes 2405 c and 2405 d can be configured tomeasure the responses of accelerometer 2500 a to z-axis acceleration.The electrodes 2405 e can be configured to detect acceleration of theaccelerometer 2600 a along the x axis, whereas the electrodes 2405 f canbe configured to detect acceleration of the accelerometer 2600 a alongthe y axis.

FIG. 29 shows an example of another alternative accelerometerimplementation for measuring in-plane and out-of-plane acceleration. Inthis example, the accelerometer 2400 c includes a conductive proof mass2410 c disposed within a decoupling frame 2910. The flexures 2615 cconnect the conductive proof mass 2410 c to the decoupling frame 2910and allow the conductive proof mass 2410 c to translate along the xaxis. Electrodes disposed on an adjacent substrate (not shown) candetect acceleration along the x axis according to changes of capacitancecaused by the movements of one or more slots 2420 b.

The decoupling frame 2910 can be disposed within an anchoring frame2915. The flexures 2620 c connect the decoupling frame 2910 to theanchoring frame 2915 and allow the decoupling frame 2910 and theconductive proof mass 2410 c to move along the y axis. Electrodesdisposed on an adjacent substrate (not shown) can detect accelerationalong the y axis according to changes of capacitance caused by themovements of one or more slots 2420 a.

A pivot 2515 b can connect the anchoring frame 2915 to a substrate 2401(not shown in FIG. 29). A moment imbalance has been created byfabricating most of the accelerometer 2600 c on one side of the pivot2515 b. An acceleration along the z axis rotates the accelerometer 2600c either towards or away from an electrode 2405 g on the substrate 2401.This rotation either increases or decreases the capacitance at theelectrode 2405 g by ΔC, as described above with reference to FIGS. 25and 27. Due to the rotation, a corresponding out-of-plane accelerationoutput signal proportional to ΔC results. The stress isolation slits2720 a may help desensitize acceleration measurements to stresses in thefilm, substrate and/or package.

Some accelerometer implementations feature plated stops that placeboundaries on the motions of the proof mass and/or flexures in order toprotect the proof mass and adjacent structures from potentially damagingovertravel and stiction. For example, referring to FIG. 28, posts may befabricated on the substrate 2401 around the perimeter of accelerometer2400 a, in order to limit the x and/or y displacement of theaccelerometer 2400 a. Similar structures may be formed underaccelerometer 2500 a, in order to prevent accelerometer 2500 a fromcontacting the electrode 2405 c, the electrode 2405 d or the substrate2101. Such implementations thereby improve reliability and shocksurvivability. These features may be fabricated during the samephotolithography and plating processes that are used to fabricate theproof mass and flexures.

FIG. 30 shows a graph depicting the relative sensitivity enabled by ofvarious materials that may be used to form an accelerometer or agyroscope. The relative sensitivity indicated in graph 3000 is based onthe theoretical comparison of sensors with identical topologies butdifferent materials, normalized to the sensitivity of a sensor made fromsilicon. The curve 3005 indicates that using a plated nickel alloy as astructural material can yield approximately three times greatersensitivity than using silicon as a structural material for a devicehaving the same design, assuming that dimensions of the two devices arethe same. The data points of the graph 3000 are based on the assumptionthat the same material is used for the proof mass and the flexures. Thewave speed is defined as the square root of: (Young's modulus/massdensity). A low Young's modulus provides a large displacement for agiven inertial force, whereas a high mass density provides a largeinertial force for a given acceleration.

FIG. 31A shows an example of a comb-finger accelerometer. Comb-fingeraccelerometers are also known as interdigitated-capacitor accelerometersor comb-drive accelerometers. The comb-finger accelerometer 3100includes the members 3102 a and 3102 b, on which the electrode “fingers”3105 a and 3105 b, respectively, are disposed. In this example, themember 3102 a is a movable member that is constrained to movesubstantially along the x axis. When the member 3102 a moves toward thestationary member 3102 b, an overlap between the fingers 3105 a and 3105b increases. Accordingly, motion of the member 3102 a in a positive xdirection results in increased capacitance between the fingers 3105 aand 3105 b.

FIG. 31B is a graph that depicts the performance of comb-drive andSLOT-based accelerometers. The relative effect of changing sacrificialgap height and proof mass thickness on the sensitivity ofcapacitive-SLOT and comb-finger based accelerometers may be observed inFIG. 31B. The curve 3115 corresponds to the comb-finger basedaccelerometer of the inset 3155, whereas the curve 3120 corresponds tothe comb-finger based accelerometer of the inset 3160. The inserts 3155and 3160 depict cross-sectional views of the comb-finger basedaccelerometers, with the fingers shown above a substrate. Insets 3155and 3160 also show examples of the dimensions and spacing of the fingers3105 a and 3105 b. The curve 3125 corresponds to the SLOT-basedaccelerometer of the inset 3165 and the curve 3130 corresponds to theSLOT-based accelerometer of the inset 3170.

The resulting graph 3110 indicates that the disclosed SLOT transducertopologies can enable high sensitivity without the need forhigh-aspect-ratio structural features. Moreover, SLOT-basedaccelerometer implementations gain efficiency over comb drive deviceswith increasing feature size. The minimum lateral feature size indicatedon the horizontal axis refers to the finger width and spacing in thecase of comb finger-type accelerometers and the width of the slot in thecase of SLOT-based accelerometers. The specific scale factor on thevertical axis refers to the change in capacitance per unit area of anaccelerometer in response to a 100 nm lateral translation of the proofmass. For relatively larger minimum lateral feature sizes (here, minimumlateral feature sizes greater than 6 microns), both examples ofSLOT-based accelerometers provide a larger change in capacitance perunit area than the comb-finger accelerometers. The SLOT-basedaccelerometer with a 1 micron gap provides a larger change incapacitance per unit area for all depicted minimum lateral featuresizes.

FIG. 32 shows a graph that depicts the performance of SLOT-basedaccelerometers having slots of various depths, including a through slotwhere the slot extends completely through the proof mass. The curves3205, 3210, 3215 and 3220 correspond to inset 3250, in which the proofmass includes a blind slot, where the slot extends partially into theproof mass. The curves 3205, 3210, 3215 and 3220 correspond toincreasing depths of such a blind slot. The curve 3225 corresponds tothe inset 3260, in which the proof mass includes a through slot.

As illustrated in FIG. 32, the performance of some of the SLOT-basedin-plane accelerometers may be enhanced by replacing the through slotsin the proof mass with blind slots. Replacing a slot that extendscompletely through the proof mass with a slot that does not extendcompletely through the proof mass can reduce the required plating aspectratio (the height to width ratio of the slot). Increasing the proof massareal density can improve the sensitivity for a given sensor area.Therefore, having relatively shallower slots also can improveaccelerometer sensitivity for a given area. From simulations, it hasbeen determined that essentially no sensitivity (ΔC/Δx) is lost if anair-filled groove is at least twice the depth of the gap between theproof mass and the underlying electrode. Sensitivity decreases withincreasing permittivity of optional groove-filling dielectric.

FIG. 33 shows an example of a flow diagram that outlines stages of amethod 3300 involving the use of one or more gyroscopes oraccelerometers in a mobile device. The components of some such mobiledevices are described below with reference to FIGS. 47A and 47B. Thesemobile devices may include a display, a processor that is configured tocommunicate with the display and a memory device that is configured tocommunicate with the processor. The processor may be configured toprocess image data.

However, the processor (and/or another such component or device) alsomay be configured for communication with one or more accelerometersand/or gyroscopes. The processor may be configured to process andanalyze gyroscope data and/or accelerometer data. In someimplementations, the mobile device may include accelerometers andgyroscopes that collectively provide an inertial sensor that isresponsive to movement corresponding to six degrees of freedom,including three linear degrees of freedom and three rotational degreesof freedom.

In block 3301, the processor may control the display for normal displayoperation. When angular rotation or linear acceleration is detected(block 3305), gyroscope data and/or accelerometer data may be providedto the processor (block 3310). In block 3315, the processor determineswhether to respond to the gyroscope data and/or accelerometer data. Forexample, the processor may decide that no response will be made unlessthe gyroscope data and/or accelerometer data indicate an angularrotation or a linear acceleration is greater than a predeterminedthreshold level of acceleration. If the gyroscope data and/oraccelerometer data do not indicate a value greater than a predeterminedthreshold, the processor may control the display according to proceduresfor normal display operation, e.g., as described above with reference toFIGS. 2 through 5B.

However, if the gyroscope data and/or accelerometer data do indicate avalue greater than the predetermined threshold (or if the processordetermines that a response is required according to another criterion),the processor will control the display, at least in part, according tothe gyroscope data and/or accelerometer data (block 3320). For example,the processor may control a state of the display according toaccelerometer data. The processor may be configured to determine whetherthe accelerometer data indicate, e.g., that the mobile device has beendropped or is being dropped. The processor may be further configured tocontrol a state of the display to prevent or mitigate damage when theaccelerometer data indicate the display has been or is being dropped.

If the accelerometer data indicate that the mobile device has beendropped, the processor also may save such accelerometer data in thememory. The processor also may be configured to save time dataassociated with the accelerometer data when the accelerometer dataindicate that the mobile device has been dropped. For example, themobile device also may include a network interface. The processor may beconfigured to obtain the time data from a time server via the networkinterface. Alternatively, the mobile device may include an internalclock.

Alternatively, or additionally, the processor may be configured tocontrol the display of a game according to accelerometer and/orgyroscope data. For example, the accelerometer and/or gyroscope data mayresult from a user's interaction with the mobile device during gameplay. The user's interaction may, for example, be in response to gameimages that are being presented on the display.

Alternatively, or additionally, the processor may be configured tocontrol the orientation of the display according to gyroscope oraccelerometer data. The processor may, for example, determine that auser has rotated the mobile device to a new device orientation and maycontrol the display according to the new device orientation. Theprocessor may determine that displayed images should be re-orientedaccording to the rotation or direction of the mobile device when adifferent portion of the mobile device is facing upward.

The processor may then determine whether the process 3300 will continue(block 3325). For example, the processor may determine whether the userhas powered off the device, whether the device should enter a “sleepmode” due to lack of user input for a predetermined period of time, etc.If the process 3300 does continue, the process 3300 may then return toblock 3301. Otherwise, the process will end (block 3330).

An example of a process for fabricating accelerometers and relatedapparatus will now be described with reference to FIGS. 34 through 40C.FIG. 34 shows an example of a flow chart that provides an overview of amethod of fabricating accelerometers. FIGS. 35A through 39B showexamples of cross-sections through a substrate, a portion of anaccelerometer and portions of structures for packaging the accelerometerand making electrical connections with the accelerometer, at variousstages during the fabrication process. FIGS. 40A through 40C showexamples cross-sectional views of various blocks in a process of forminga device that includes a MEMS die and an integrated circuit.

Referring to FIG. 34, some operations of a method 3400 will bedescribed. The process flow of method 3400 allows a first set ofoperations to be performed at, e.g., a facility having the ability tobuild MEMS devices (or similar devices) on large-area substrates, suchas large-area glass panels. Such a facility may, for example, be a Gen 5“fab,” having the capability of fabricating devices on 1100 mm by 1300mm substrates, or a Gen 6 fab, having the capability of fabricatingdevices on 1500 mm by 1850 mm substrates.

Accordingly, in block 3401, pass-through metallization and accelerometerelectrodes are formed on a large-area substrate, which is a large-areaglass substrate in this example. In block 3405 a plurality of featuresfor accelerometers and related structures are formed on the large-areasubstrate. In some implementations, the features for hundreds ofthousands or more of such devices may be formed on a single large-areasubstrate. In some implementations, the accelerometers and gyroscopesmay have a die size less than about 1 mm on a side to 3 mm on a side ormore. The related structures may, for example, include electrodes,electrical pads, structures for encapsulation (such as seal ringstructures), etc. Examples of such processes will be described belowwith reference to FIGS. 35A through 38D.

In block 3410 of FIG. 34, the partially-fabricated accelerometers andother devices are prepared for a subsequent electroplating process. Asdescribed below with reference to FIG. 38A, block 3410 may involvedepositing a seed layer such as nickel, a nickel alloy, copper, orchrome/gold and the formation of thick layers of high aspect ratiolithography material for subsequent plating.

According to method 3400, the accelerometers and other structures areonly partially fabricated on the large-area glass substrates. One reasonfor this partial fabrication is that there are currently few platingfacilities that could process even Gen 4 or Gen 5 substrate sizes.However, there are many plating facilities that can handle smallersubstrates, such as Gen 2 substrates (350 mm by 450 mm). Therefore, inblock 3415, the large-area glass substrate on which the accelerometersand other structures have been partially fabricated is divided intosub-panels for the electroplating process(es).

In block 3420, the electroplating process(es) are performed. Theseprocesses are described below with reference to FIG. 38B. Theelectroplating process may, in some implementations, involve depositingmost of the metal of each accelerometer's proof mass, frame, anchor(s)and other structures. The high aspect ratio lithography material maythen be removed and the sacrificial material may be removed to releaseeach accelerometer's proof mass and frame (block 3425). Examples ofthese operations are described below with reference to FIGS. 38C and38D.

Block 3430 involves optional accelerometer encapsulation, as well assingulation (e.g., by dicing) and other processes. In someimplementations, the method 3400 may involve attaching an integratedcircuit to an encapsulated accelerometer, forming electrical connectionswith another substrate, molding and singulation. These processes aredescribed below with reference to FIGS. 39A through 40C.

Referring now to FIG. 35A, a process of fabricating accelerometers willbe described in more detail. FIG. 35A depicts a cross-section throughone small portion (e.g., on the order of a few millimeters) of alarge-area substrate 3505, which is a glass substrate in this example.At this stage, a metallization layer 3510 such as a chromium (Cr)/gold(Au) layer has been deposited on the large-area substrate 3505. Otherconductive materials may be used instead of Cr and/or Au, such as one ormore of aluminum (Al), titanium (Ti), tantalum (Ta), tantalum nitride(TaN), platinum (Pt), silver (Ag), nickel (Ni), doped silicon or TiW .

The metallization layer 3510 may then be patterned and etched, e.g. asshown in FIG. 35B. In this example, the central portion of themetallization layer 3510 has been patterned and etched to form theelectrode area 3510 b, which will form part of an accelerometer. Theaccelerometer and/or other devices may, for example, be sealed inside acavity formed between the metallization areas 3510 a. The metallizationareas 3510 a can form the “pass through” electrical connection frominside such packaging to outside the packaging. The metallization areas3510 a also can allow an electrical connection to be made between thesedevices and other devices outside the packaging.

FIG. 35C depicts a dielectric layer 3515 that is deposited over themetallization layer 3510. The dielectric layer 3515, which may be SiO₂SiON, Si₃N₄ or another suitable dielectric, may then be patterned andetched to form openings 3605 a, 3605 b, 3605 c and 3605 d through thedielectric layer 3515 to the metallization areas 3510 a (see FIG. 36A).

At the stage depicted in FIG. 36B, a metallization layer 3610 has beendeposited on the dielectric layer 3515 and into the openings 3605 a,3605 b, 3605 c and 3605 d. The metallization layer 3610 may be formed ofany appropriate conductive material, such as Cr, Au, Al, Ti, Ta, TaN,Pt, Ag, Ni, doped silicon or TiW.

The metallization layer 3610 is then patterned and etched, as shown inFIG. 36C. As a result, the lead areas 3615 a and 3615 b are exposedabove the surface of the dielectric layer 3515 and are configured forelectrical connectivity with the metallization areas 3510 a. Similarly,the accelerometer base areas 3625 a and 3625 b (which may be anchorareas in some implementations) also remain above the surface of thedielectric layer 3515 and configured for electrical connectivity withthe metallization areas 3510 a. The seal ring areas 3620 a and 3620 balso can be above the surface of the dielectric layer 3515, but are notelectrically connected to the metallization areas 3510 a. At the stageshown in FIG. 36D, the dielectric layer 3515 has been removed from theelectrode area 3510 b.

FIG. 37A illustrates a stage after which a sacrificial layer 3705 hasbeen deposited. In this example, the sacrificial layer 3705 is formed ofMoCr, but other materials may be used for the sacrificial layer 3705,such as Cu. FIG. 37B illustrates a stage of the process after thesacrificial layer 3705 has been patterned and etched. At this stage, thelead areas 3615 a and 3615 b, the seal ring areas 3620 a and 3620 b, andthe accelerometer base areas 3625 a and 3625 b are exposed. A portion ofthe sacrificial layer 3705 remains over the electrode area 3510 b.

The partially-fabricated accelerometer and related structures are thenprepared for electroplating. In some implementations, a plating seedlayer may be deposited prior to the electroplating process(es) asdescribed above. The seed layer may, for example, be formed by asputtering process and may be formed of nickel, a nickel alloy (such asnickel iron, nickel cobalt or nickel manganese), copper, or chrome/gold.As shown in FIG. 38A, a thick layer of high aspect ratio lithographymaterial 3805 such as photoresist is formed over areas on which metalwill not subsequently be electroplated. The high aspect ratiolithography material 3805 may be selectively exposed through a photomaskand developed to form a mold that will define the shapes of metalstructures that are subsequently plated up through the mold during theelectroplating process(es). According to some implementations, the layerof high aspect ratio lithography material 3805 is tens of microns thick,e.g., 10 to 50 microns thick or more. In other implementations, thelayer of high aspect ratio lithography material 3805 can be thicker orthinner depending on the desired configuration of the, e.g.,accelerometer. The high aspect ratio lithography material 3805 may beany of various commercially-available high aspect ratio lithographymaterials, such as KMPR® photoresist provided by Micro-Chem or MTF™WBR2050 photoresist provided by DuPont®.

The thick layers of the high aspect ratio lithography material 3805 canbe formed over the lead areas 3615 a and 3615 b, the seal ring areas3620 a and 3620 b, and over selected areas of the portion of thesacrificial layer 3705 that is still remaining. The selected areas areareas of the sacrificial layer 3705 that will not be electroplated. Thegaps 3810 expose accelerometer base areas 3625 a and 3625 b, as well asother areas above the sacrificial layer 3705.

The large-area substrate on which the above-described structures havebeen partially formed may be divided into smaller sub-panels prior tothe electroplating process. In this example, the large-area glasssubstrate is scribed and broken, but the large-area glass substrate maybe divided in any appropriate manner, such as by sawing or dicing.

FIG. 38B depicts the apparatus after a thick metal layer 3815 has beenelectroplated in the areas between structures formed by the high aspectratio lithography material 3805. In some implementations, the thickmetal layer 3815 may be tens of microns thick, e.g., 5 to 50 micronsthick. In other implementations, the thick metal layer 3815 can bethicker or thinner depending on the desired configuration of the, e.g.,accelerometer. In this example, the thick metal layer 3815 is formed ofa nickel alloy, but in other implementations, the thick metal layer 3815may be formed of plated nickel, electroless nickel, CoFe, Fe basedalloys, NiW, NiRe, PdNi, PdCo or other electroplated materials. In someimplementations, a thin gold layer may be deposited on the thick metallayer 3815, primarily to resist corrosion.

FIG. 38C depicts the deposition of the thick metal layer 3815 and theremoval of the high aspect ratio lithography material 3805. Removing thehigh aspect ratio lithography material 3805 exposes the lead areas 3615a and 3615 b, the seal ring areas 3620 a and 3620 b, and selected areasof the sacrificial layer 3705. The sacrificial layer 3705 may then beetched, e.g., by a wet etching process or a plasma etching process, torelease the moveable area 3840 of the accelerometer 3850 (see FIG. 38D)using, for example, XeF₂ for a molybdenum or molychrome sacrificiallayer or a copper etchant for a copper sacrificial layer. Wet etching ofCu to selectively etch Cu without etching nickel alloys, Cr or Au may,for example, be accomplished either by using a combination of hydrogenperoxide and acetic acid, or by using ammoniacal Cu etchants that arecommonly used in the printed circuit board industry. The moveable area3840 may, for example, include a proof mass and/or frame such as thosedescribed above. During the operation of the accelerometer 3850, motionof the gaps 3860 may induce changes in capacitance that are detected bythe electrodes 3510 b.

FIG. 39A illustrates the result of a subsequent encapsulation processaccording to one example. Here, a cover 3905 has been attached to theseal ring areas 3620 a and 3620 b in order to encapsulate theaccelerometer 3850. In some implementations, the cover 3905 may be aglass cover, a metal cover, etc. The cover 3905 may be one of aplurality of covers formed on another substrate. In this example, thecover includes a plurality of cover portions 3905 a that can form anenclosure around the accelerometer 3850. In this example, the coverportions 3905 a are connected by the cover areas 3905 b. The coverportions 3905 a may be attached to the seal ring areas 3620 a and 3620b, for example, by a soldering or eutectic bonding process, or by anadhesive such as an epoxy. In some implementations, the cover portions3905 a may completely enclose the accelerometer 3850, whereas in otherimplementations the cover portions 3905 a may only partially enclose theaccelerometer 3850. In this example, the lead areas 3615 a and 3615 bremain outside of the area encapsulated by the cover 3905, allowing aconvenient electrical connection to the accelerometer 3850.

In some implementations, portions of the cover 3905 may be removed. Forexample, at least part of the cover areas 3905 b may be removed (by adicing process, for example) to allow more convenient access to the leadareas 3615 a and 3615 b (see FIG. 39B). The thickness of the resultingencapsulated accelerometer 3910 may also be reduced, if desired. In thisexample, a chemical-mechanical planarization (CMP) process is used tothin the substrate 3505. In some implementations, the encapsulatedaccelerometer 3910 may be thinned to an overall thickness of less than 1mm, and more specifically to 0.7 mm or less. The resulting encapsulatedaccelerometer 3910 may be singulated, e.g., by dicing.

FIG. 40A depicts an apparatus formed by combining the encapsulatedaccelerometer 3910 with an integrated circuit 4005 and attaching bothdevices to another substrate 4015, which is a printed circuit board inthis example. In this illustration, the integrated circuit 4005 isattached to the encapsulated accelerometer 3910 by a soldering process(see solder layer 4010). Similarly, the encapsulated accelerometer 3910is attached to the substrate 4015 by a soldering process (see solderlayer 4020). Alternatively, the integrated circuit 4005 may be attachedto the accelerometer 3910 by an adhesive, such as epoxy.

FIG. 40B depicts wire bonds 4025, which are used to make electricalconnections between the integrated circuit 4005 and the encapsulatedaccelerometer 3910, and between the encapsulated accelerometer 3910 andthe substrate 4015. In alternative implementations, the encapsulatedaccelerometer 3910 may include vias through the substrate 3905 that areconfigured to form electrical connections by surface mounting.

At the stage depicted in FIG. 40C, the integrated circuit 4005 and theencapsulated accelerometer 3910 have been encapsulated with a protectivematerial 4030, which may be a dielectric material such as a polymer, aninjection molded material such as liquid crystal polymer (LCP), SiO2 orSiON. In this example, the substrate 4015 includes electrical connectors4035 that are configured for mounting onto a printed circuit board orother apparatus. The resulting package 4040 is therefore configured forsurface-mount technology.

An example of a process for fabricating a gyroscope and relatedapparatus will now be described with reference to FIGS. 41 through 46B.FIG. 41 shows an example of a flow diagram that provides an overview ofthe process for fabricating gyroscopes and related structures. FIGS. 42Athrough 46B show examples of cross-sectional views through a substrate,a portion of a gyroscope and portions of structures for packaging thegyroscope and making electrical connections with the gyroscope, atvarious stages during the process outlined in FIG. 41.

Referring to FIG. 41, some operations of a method 4100 will bedescribed. The process flow of method 4100 allows a first set ofoperations to be performed at a facility having the ability to buildMEMS and similar devices on large-area substrates, such as large-areaglass panels. Such a facility may, for example, be a Gen 5 fab or a Gen6 fab. Accordingly, in block 4105 a large number of gyroscope featuresand related structures are formed on a large-area substrate. Forexample, hundreds of thousands or more of such structures could befabricated on a large-area substrate. The related structures mayinclude, for example, electrodes, electrical pads, structures forencapsulation (such as seal ring structures), etc. Examples of suchprocesses will be described below with reference to FIGS. 42A through44B.

In block 4110 of FIG. 41, the partially-fabricated gyroscopes and otherdevices are prepared for a subsequent electroplating process. Asdescribed below with reference to FIGS. 44B and 44C, block 4110 mayinvolve plating seed layer deposition and the formation of thick layersof high aspect ratio lithography material such as photoresist.

According to the method 4100, the gyroscopes and other structures areonly partially fabricated on the large-area glass substrates. One reasonfor this partial fabrication is that there are currently few platingfacilities that could process the Gen 4 or Gen 5 substrate sizes.However, there are many plating facilities that can handle smallersubstrates, such as Gen 2 substrates. Therefore, in block 4115, thelarge-area glass substrate on which the gyroscopes and other structureshave been partially fabricated is divided into sub-panels for theelectroplating procedure(s).

In block 4120, the electroplating process(es) will be performed. Theseprocesses are described below with reference to FIG. 45A. Theelectroplating process may, in some implementations, involve depositingmost of the metal of each gyroscope's proof mass, frame and otherstructures. The high aspect ratio lithography material may then beremoved and the sacrificial material may be removed to release eachgyroscope's proof mass and frame (block 4125). Examples of theseoperations are described below with reference to FIGS. 45B and 46A.

Block 4130 may involve gyroscope encapsulation, as well as singulation(e.g., by dicing) and other processes. These processes are describedbelow with reference to FIG. 46B.

FIG. 42A depicts a cross-section through a large-area substrate 4200,which is a glass substrate in this example. The large-area glasssubstrate 4200 has a metallization layer 4205, which is a Cr/Au layer inthis example, deposited on it. Other conductive materials may be usedinstead of chrome and/or gold, such as Al, TiW, Pt, Ag, Ni, nickelalloys in Co, Fe or Mn, Ti/Au, Ta/Au or doped silicon. The metallizationlayer 4205 may be patterned and etched, e.g. as shown in FIG. 42A. Themetallization layer 4205 can be used to form the “pass through”electrical connection from inside the seal ring to outside the sealring. Gyroscope(s) and/or other devices may, for example, be sealedinside a cavity inside the packaging. The metallization layer 4205allows an electrical connection to be made between these devices andother devices outside the packaging.

FIG. 42B depicts a dielectric layer 4215 such as SiO₂, SiON or otherdielectric material that is deposited over the metallization layer 4205.The dielectric layer 4215 may then be etched to form openings 4220 a,4220 b and 4220 c through the dielectric layer 4215 to the metallizationlayer 4205.

FIG. 42C illustrates a stage after which a sacrificial layer 4225 hasbeen deposited. In this example, the sacrificial layer 4225 is formed ofMoCr, but other materials may be used for the sacrificial layer 4225such as copper or deposited amorphous or polycrystalline silicon. FIG.42D illustrates areas of the sacrificial layer 4225 remaining after thesacrificial layer 4225 has been patterned and etched.

FIG. 43A illustrates a stage after which a dielectric layer 4305 hasbeen deposited on the sacrificial layer 4225. Moreover, the dielectriclayer 4305 has been patterned and etched. In FIG. 43B, a metallizationlayer 4310 is then deposited, patterned and etched. In this example, themetallization layer 4310 is in contact with the metallization layer 4205in an anchor area 4315.

In FIG. 43C shows an example of a piezoelectric film 4320 that has beendeposited, patterned and etched. In this example, the piezoelectric film4320 is formed of aluminum nitride, but other piezoelectric materialsmay be used such as ZnO or lead zirconate titanate (PZT). In FIG. 43D, ametallization layer 4325 is deposited, patterned and etched. Here, themetallization layer 4325 forms a top layer of the electrode 4330, whichmay be a piezoelectric drive electrode or a piezoelectric senseelectrode, depending on the implementation.

FIG. 44A shows an example of a dielectric layer 4405 that has beendeposited, patterned and etched. During this phase, the dielectric layer4405 is removed from most areas shown in FIG. 44A except the anchor area4315 and the area adjacent to the electrode 4330.

At this stage, the partially-fabricated gyroscope components and relatedstructures can be prepared for one or more electroplating processes.FIG. 44B shows an example of a plating seed layer 4405 such as nickel, anickel alloy, copper, or chrome/gold that can be deposited prior to theelectroplating process. As depicted in FIG. 44C, after the plating seedlayer 4405 is deposited, a thick layer of high aspect ratio lithographymaterial 4410 such as a thick photoresist can be formed between a proofmass area 4415 and a frame area 4420. According to some implementations,the layer of high aspect ratio lithography material 4410 is tens ofmicrons thick, e.g., 40 to 50 microns thick. In other implementations,the layer of high aspect ratio lithography material 4410 can be thickeror thinner depending on the desired configuration of the, e.g.,gyroscope. The high aspect ratio lithography material 4410 may be any ofvarious commercially-available high aspect ratio lithography materials,such as KMPR® photoresist provided by Micro-Chem or MTF™ WBR2050photoresist provided by DuPont®. Thick layers of the high aspect ratiolithography material 4410 also can be formed between the frame area 4420and the seal ring area 4425, as well as between the seal ring area 4425and the electrical pad area 4430. The high aspect ratio lithographymaterial 4410 may be exposed with a suitable photomask and developed todefine the shapes of electroplated metal structures that aresubsequently formed.

As noted above, the large-area substrate on which the above-describedstructures have been partially formed may be divided into smallersub-panels prior to the electroplating process. In this example, thelarge-area glass substrate is scribed and broken, but the large-areaglass substrate may be divided in any appropriate manner (such as bydicing).

As shown in FIG. 45A, a thick metal layer 4505 may be electroplated inthe areas between the high aspect ratio lithography material 4410. Inthis example, the thick metal layer 4505 is formed of a nickel alloy,but in other implementations thick metal layer 4505 may be formed ofnickel or other plated metal alloys such as cobalt-iron,nickel-tungsten, palladium-nickel or palladium-cobalt. Here, a thin goldlayer 4510 is deposited on the thick metal layer 4505, primarily toresist corrosion of the thick metal layer 4505. The gold layer 4510 alsomay be formed by an electroplating process.

As depicted in FIG. 45B, after these metal layers have been deposited,the high aspect ratio lithography material 4410 can be removed frombetween the regions where the thick metal layer 4505 has been deposited.Removing the high aspect ratio lithography material 4410 exposesportions of the seed layer 4405, which may then be etched away to exposethe sacrificial material 4225. FIG. 46A depicts the sacrificial material4225 etched away, e.g., by a wet etching process or a plasma etchingprocess, to release the proof mass 4605 and the frame 4610.

FIG. 46B illustrates the result of an encapsulation process, accordingto one example. Here, a cover 4615 has been attached to the seal ring4620 in order to encapsulate the gyroscope 4625. In someimplementations, the cover 4615 may be a glass cover, a metal cover,etc. The cover 4615 may be attached to the seal ring 4620, for example,by a soldering process or by an adhesive, such as epoxy. An electricalpad 4630 remains outside of the area encapsulated by the cover 4615,allowing a convenient electrical connection to the gyroscope 4625 viathe metallization layer 4205.

The gyroscope 4625 resulting from this example of a fabrication processmay, for example, correspond with the drive frame x-axis gyroscope 1200shown in FIG. 12 and described above. The anchor 4635 of the gyroscope4625 may correspond with the central anchor 1205 shown in FIG. 12. Theelectrode 4330 may correspond with a drive electrode 1215 shown in FIG.12. The proof mass 4605 may correspond with the drive frame 1210 of FIG.12, whereas the frame 4610 may correspond with the proof mass 1220 ofFIG. 12.

As another example, the gyroscope 4625 may correspond with the z-axisgyroscope 2000 shown in FIG. 20A et seq. The anchor 4635 of thegyroscope 4625 may correspond with the central anchor 2005 shown in FIG.20A et seq. Electrode 4330 may correspond with one of sense electrodes2020 a-d. The proof mass 4605 may correspond with the sense frame 2010of FIG. 20A, whereas the frame 4610 may correspond with the drive frame2030 of FIG. 20A.

Although the processes of fabricating gyroscopes and accelerometers havebeen described separately, large numbers of both types of devices may beformed on the same large-area substrate, if so desired. Theaccelerometers described herein may, for example, be formed by using asubset of the processes for fabricating gyroscopes. For example, theaccelerometers described herein do not require piezoelectric driveelectrodes or piezoelectric sense electrodes. Accordingly, nopiezoelectric layer is required when fabricating such accelerometers. Ifaccelerometers and gyroscopes are being fabricated on the samelarge-area substrate, the accelerometer portion(s) may be masked offwhen the piezoelectric layer is being deposited, patterned and etched.

In some implementations, the gyroscopes and accelerometers describedherein may use different thicknesses of sacrificial material for theirfabrication. For example, the gap between the accelerometer electrodesand the proof mass may be larger, in some implementations, than the gapbetween the proof mass and the metallization layer of a gyroscope. Insome implementations that use copper as a sacrificial material, thisdifference in sacrificial layer thickness may be produced by platingcopper on the copper seed layer only in those areas where accelerometersare being fabricated.

In some gyroscope implementations, the gyroscope may be encapsulated ina vacuum, whereas accelerometers do not need to be encapsulated in avacuum. In some implementations, having gas in the encapsulatedaccelerometers may actually be beneficial, because it provides damping.Therefore, in some implementations, two different encapsulationprocesses may be used when fabricating both gyroscopes andaccelerometers on a large-area substrate. One encapsulation process maybe performed substantially in a vacuum, whereas the other would not beperformed in a vacuum. In other implementations, a single encapsulationprocess may be performed substantially in a vacuum. The encapsulatedaccelerometers may be left partially open during this process, so thatgas could subsequently enter the encapsulated accelerometers' packaging.The accelerometers' packaging could be entirely enclosed (e.g., withsolder) during a subsequent process, if so desired.

FIGS. 47A and 47B show examples of system block diagrams illustrating adisplay device 40 that includes a plurality of interferometricmodulators. The display device 40 can be, for example, a cellular ormobile telephone. However, the same components of the display device 40or slight variations thereof are also illustrative of various types ofdisplay devices such as televisions, e-readers and portable mediaplayers.

The display device 40 includes a housing 41, a display 30, an antenna43, a speaker 45, an input device 48, and a microphone 46. The housing41 can be formed from any of a variety of manufacturing processes,including injection molding, and vacuum forming. In addition, thehousing 41 may be made from any of a variety of materials, including,but not limited to: plastic, metal, glass, rubber, and ceramic, or acombination thereof. The housing 41 can include removable portions (notshown) that may be interchanged with other removable portions ofdifferent color, or containing different logos, pictures, or symbols.

The display 30 may be any of a variety of displays, including abi-stable or analog display, as described herein. The display 30 alsocan be configured to include a flat-panel display, such as plasma, EL,OLED, STN LCD, or TFT LCD, or a non-flat-panel display, such as a CRT orother tube device. In addition, the display 30 can include aninterferometric modulator display, as described herein.

The components of the display device 40 are schematically illustrated inFIG. 47B. The display device 40 includes a housing 41 and can includeadditional components at least partially enclosed therein. For example,the display device 40 includes a network interface 27 that includes anantenna 43 which is coupled to a transceiver 47. The transceiver 47 isconnected to a processor 21, which is connected to conditioning hardware52. The conditioning hardware 52 may be configured to condition a signal(e.g., filter a signal). The conditioning hardware 52 is connected to aspeaker 45 and a microphone 46. The processor 21 is also connected to aninput device 48 and a driver controller 29. The driver controller 29 iscoupled to a frame buffer 28, and to an array driver 22, which in turnis coupled to a display array 30. A power supply 50 can provide power toall components as required by the particular display device 40 design.The network interface 27 includes the antenna 43 and the transceiver 47so that the display device 40 can communicate with one or more devicesover a network. The network interface 27 also may have some processingcapabilities to relieve, e.g., data processing requirements of theprocessor 21. The antenna 43 can transmit and receive signals. In someimplementations, the antenna 43 transmits and receives RF signalsaccording to the IEEE 16.11 standard, including IEEE 16.11(a), (b), or(g), or the IEEE 802.11 standard, including IEEE 802.11a, b, g or n. Insome other implementations, the antenna 43 transmits and receives RFsignals according to the BLUETOOTH standard. In the case of a cellulartelephone, the antenna 43 is designed to receive code division multipleaccess (CDMA), frequency division multiple access (FDMA), time divisionmultiple access (TDMA), Global System for Mobile communications (GSM),GSM/General Packet Radio Service (GPRS), Enhanced Data GSM Environment(EDGE), Terrestrial Trunked Radio (TETRA), Wideband-CDMA (W-CDMA),Evolution Data Optimized (EV-DO), 1×EV-DO, EV-DO Rev A, EV-DO Rev B,High Speed Packet Access (HSPA), High Speed Downlink Packet Access(HSDPA), High Speed Uplink Packet Access (HSUPA), Evolved High SpeedPacket Access (HSPA+), Long Term Evolution (LTE), AMPS, or other knownsignals that are used to communicate within a wireless network, such asa system utilizing 3G or 4G technology. The transceiver 47 canpre-process the signals received from the antenna 43 so that they may bereceived by and further manipulated by the processor 21. The transceiver47 also can process signals received from the processor 21 so that theymay be transmitted from the display device 40 via the antenna 43. Theprocessor 21 may be configured to receive time data, e.g., from a timeserver, via the network interface 27.

In some implementations, the transceiver 47 can be replaced by areceiver. In addition, the network interface 27 can be replaced by animage source, which can store or generate image data to be sent to theprocessor 21. The processor 21 can control the overall operation of thedisplay device 40. The processor 21 receives data, such as compressedimage data from the network interface 27 or an image source, andprocesses the data into raw image data or into a format that is readilyprocessed into raw image data. The processor 21 can send the processeddata to the driver controller 29 or to the frame buffer 28 for storage.Raw data typically refers to the information that identifies the imagecharacteristics at each location within an image. For example, suchimage characteristics can include color, saturation, and gray-scalelevel.

The processor 21 can include a microcontroller, CPU, or logic unit tocontrol operation of the display device 40. The conditioning hardware 52may include amplifiers and filters for transmitting signals to thespeaker 45, and for receiving signals from the microphone 46. Theconditioning hardware 52 may be discrete components within the displaydevice 40, or may be incorporated within the processor 21 or othercomponents.

In some implementations, the display device 40 may include one or moregyroscopes and/or accelerometers 75. Such gyroscopes and/oraccelerometers 75 may, for example, be substantially as described hereinand may be made according to processes described herein. The gyroscopesand/or accelerometers 75 may be configured for communication with theprocessor 21, in order to provide gyroscope data or accelerometer datato the processor 21. Accordingly, display device 40 may be able toperform some of the above-described methods relating to the use ofgyroscope data and/or accelerometer data. Moreover, such data may bestored in a memory of the display device 40.

The driver controller 29 can take the raw image data generated by theprocessor 21 either directly from the processor 21 or from the framebuffer 28 and can re-format the raw image data appropriately for highspeed transmission to the array driver 22. In some implementations, thedriver controller 29 can re-format the raw image data into a data flowhaving a raster-like format, such that it has a time order suitable forscanning across the display array 30. Then the driver controller 29sends the formatted information to the array driver 22. Although adriver controller 29, such as an LCD controller, is often associatedwith the system processor 21 as a stand-alone integrated circuit (IC),such controllers may be implemented in many ways. For example,controllers may be embedded in the processor 21 as hardware, embedded inthe processor 21 as software, or fully integrated in hardware with thearray driver 22.

The array driver 22 can receive the formatted information from thedriver controller 29 and can re-format the video data into a parallelset of waveforms that are applied many times per second to the hundreds,and sometimes thousands (or more), of leads coming from the display'sx-y matrix of pixels.

In some implementations, the driver controller 29, the array driver 22,and the display array 30 are appropriate for any of the types ofdisplays described herein. For example, the driver controller 29 can bea conventional display controller or a bi-stable display controller(e.g., an IMOD controller). Additionally, the array driver 22 can be aconventional driver or a bi-stable display driver (e.g., an IMOD displaydriver). Moreover, the display array 30 can be a conventional displayarray or a bi-stable display array (e.g., a display including an arrayof IMODs). In some implementations, the driver controller 29 can beintegrated with the array driver 22. Such an implementation is common inhighly integrated systems such as cellular phones, watches and othersmall-area displays.

In some implementations, the input device 48 can be configured to allow,e.g., a user to control the operation of the display device 40. Theinput device 48 can include a keypad, such as a QWERTY keyboard or atelephone keypad, a button, a switch, a rocker, a touch-sensitivescreen, or a pressure- or heat-sensitive membrane. The microphone 46 canbe configured as an input device for the display device 40. In someimplementations, voice commands through the microphone 46 can be usedfor controlling operations of the display device 40.

The power supply 50 can include a variety of energy storage devices asare well known in the art. For example, the power supply 50 can be arechargeable battery, such as a nickel-cadmium battery or a lithium-ionbattery. The power supply 50 also can be a renewable energy source, acapacitor, or a solar cell, including a plastic solar cell or solar-cellpaint. The power supply 50 also can be configured to receive power froma wall outlet.

In some implementations, control programmability resides in the drivercontroller 29 which can be located in several places in the electronicdisplay system. In some other implementations, control programmabilityresides in the array driver 22. The above-described optimization may beimplemented in any number of hardware and/or software components and invarious configurations.

The various illustrative logics, logical blocks, modules, circuits andalgorithm processes described in connection with the implementationsdisclosed herein may be implemented as electronic hardware, computersoftware, or combinations of both. The interchangeability of hardwareand software has been described generally, in terms of functionality,and illustrated in the various illustrative components, blocks, modules,circuits and processes described above. Whether such functionality isimplemented in hardware or software depends upon the particularapplication and design constraints imposed on the overall system.

The hardware and data processing apparatus used to implement the variousillustrative logics, logical blocks, modules and circuits described inconnection with the aspects disclosed herein may be implemented orperformed with a general purpose single- or multi-chip processor, adigital signal processor (DSP), an application specific integratedcircuit (ASIC), a field programmable gate array (FPGA) or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, or any combination thereof designed to perform thefunctions described herein. A general purpose processor may be amicroprocessor, or, any conventional processor, controller,microcontroller, or state machine. A processor may also be implementedas a combination of computing devices, e.g., a combination of a DSP anda microprocessor, a plurality of microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration. In some implementations, particular processes and methodsmay be performed by circuitry that is specific to a given function.

In one or more aspects, the functions described may be implemented inhardware, digital electronic circuitry, computer software, firmware,including the structures disclosed in this specification and theirstructural equivalents thereof, or in any combination thereof.Implementations of the subject matter described in this specificationalso can be implemented as one or more computer programs, i.e., one ormore modules of computer program instructions, encoded on a computerstorage media for execution by, or to control the operation of, dataprocessing apparatus.

The various illustrative logics, logical blocks, modules, circuits andalgorithm processes described in connection with the implementationsdisclosed herein may be implemented as electronic hardware, computersoftware, or combinations of both. The interchangeability of hardwareand software has been described generally, in terms of functionality,and illustrated in the various illustrative components, blocks, modules,circuits and processes described above. Whether such functionality isimplemented in hardware or software depends upon the particularapplication and design constraints imposed on the overall system.

The hardware and data processing apparatus used to implement the variousillustrative logics, logical blocks, modules and circuits described inconnection with the aspects disclosed herein may be implemented orperformed with a general purpose single- or multi-chip processor, adigital signal processor (DSP), an application specific integratedcircuit (ASIC), a field programmable gate array (FPGA) or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, or any combination thereof designed to perform thefunctions described herein. A general purpose processor may be amicroprocessor, or, any conventional processor, controller,microcontroller, or state machine. A processor may also be implementedas a combination of computing devices, e.g., a combination of a DSP anda microprocessor, a plurality of microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration. In some implementations, particular processes and methodsmay be performed by circuitry that is specific to a given function.

In one or more aspects, the functions described may be implemented inhardware, digital electronic circuitry, computer software, firmware,including the structures disclosed in this specification and theirstructural equivalents thereof, or in any combination thereof.Implementations of the subject matter described in this specificationalso can be implemented as one or more computer programs, i.e., one ormore modules of computer program instructions, encoded on a computerstorage media for execution by, or to control the operation of, dataprocessing apparatus.

If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. The processes of a method or algorithmdisclosed herein may be implemented in a processor-executable softwaremodule which may reside on a computer-readable medium. Computer-readablemedia includes both computer storage media and communication mediaincluding any medium that can be enabled to transfer a computer programfrom one place to another. A storage media may be any available mediathat may be accessed by a computer. By way of example, and notlimitation, such computer-readable media may include RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that may be used to storedesired program code in the form of instructions or data structures andthat may be accessed by a computer. Also, any connection can be properlytermed a computer-readable medium. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk, and blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Combinations of the above should also be included within the scope ofcomputer-readable media. Additionally, the operations of a method oralgorithm may reside as one or any combination or set of codes andinstructions on a machine readable medium and computer-readable medium,which may be incorporated into a computer program product.

Various modifications to the implementations described in thisdisclosure may be readily apparent to those skilled in the art, and thegeneric principles defined herein may be applied to otherimplementations without departing from the spirit or scope of thisdisclosure. Thus, the disclosure is not intended to be limited to theimplementations shown herein, but is to be accorded the widest scopeconsistent with the claims, the principles and the novel featuresdisclosed herein. The word “exemplary” is used exclusively herein tomean “serving as an example, instance, or illustration.” Anyimplementation described herein as “exemplary” is not necessarily to beconstrued as preferred or advantageous over other implementations.Additionally, a person having ordinary skill in the art will readilyappreciate, the terms “upper” and “lower” are sometimes used for ease ofdescribing the figures, and indicate relative positions corresponding tothe orientation of the figure on a properly oriented page, and may notreflect the proper orientation of the IMOD (or any other device) asimplemented.

Certain features that are described in this specification in the contextof separate implementations also can be implemented in combination in asingle implementation. Conversely, various features that are describedin the context of a single implementation also can be implemented inmultiple implementations separately or in any suitable subcombination.Moreover, although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Further, the drawings may schematically depict one more exampleprocesses in the form of a flow diagram. However, other operations thatare not depicted can be incorporated in the example processes that areschematically illustrated. For example, one or more additionaloperations can be performed before, after, simultaneously, or betweenany of the illustrated operations. In certain circumstances,multitasking and parallel processing may be advantageous. Moreover, theseparation of various system components in the implementations describedabove should not be understood as requiring such separation in allimplementations, and it should be understood that the described programcomponents and systems can generally be integrated together in a singlesoftware product or packaged into multiple software products.Additionally, other implementations are within the scope of thefollowing claims. In some cases, the actions recited in the claims canbe performed in a different order and still achieve desirable results.

What is claimed is:
 1. A method of fabricating a gyroscope, the methodcomprising: depositing conductive material on a substrate; forming ananchor on the substrate; forming a drive frame on the anchor; formingpairs of drive beams on opposing sides of the anchor, the drive beamsconnecting the drive frame to the anchor, the drive beams beingconfigured to constrain the drive frame to rotate substantially in aplane of the drive beams; forming a proof mass around the drive frame;and forming a plurality of sense beams that connect the drive frame tothe proof mass, the sense beams being tapered sense beams having a widththat decreases with increasing distance from the anchor, the taperedsense beams being configured to allow sense motions of the proof mass ina sense plane substantially perpendicular to the plane of the drivebeams in response to an applied angular rotation.
 2. The method of claim1, wherein forming the drive beams includes the following: depositing afirst metal layer that is in contact with the conductive material;depositing a piezoelectric layer on the first metal layer; depositing asecond metal layer on the piezoelectric layer; and forming a third metallayer on the second metal layer.
 3. The method of claim 2, whereinforming the third metal layer involves electroplating.
 4. The method ofclaim 3, wherein the electroplating involves depositing metal for theproof mass and the tapered sense beams.
 5. The method of claim 3,further including separating the substrate into a plurality ofsub-panels prior to the electroplating.
 6. The method of claim 2,wherein forming the third metal layer involves forming the third metallayer to a thickness of tens of microns.
 7. The method of claim 2,wherein forming the third metal layer involves forming at least one ofnickel, nickel-iron, nickel-cobalt, nickel-manganese, cobalt-iron,nickel-tungsten, palladium-nickel or palladium-cobalt on the secondmetal layer.
 8. The method of claim 2, further comprising: depositing agold layer on the third metal layer.
 9. The method of claim 1, whereinforming the anchor includes: etching through a sacrificial layer toexpose a first metal layer; depositing an oxide layer on the first metallayer; forming a seed layer on the oxide layer; and electroplating asecond metal layer on the seed layer.
 10. The method of claim 9, whereinforming the seed layer involves forming at least one of nickel, a nickelalloy, copper or an alloy of chrome and gold on the oxide layer.
 11. Themethod of claim 1, further comprising: encapsulating the gyroscopeinside packaging.
 12. The method of claim 11, wherein the encapsulatinginvolves sealing the gyroscope inside the packaging.
 13. The method ofclaim 12, wherein the sealing involves sealing the gyroscopesubstantially in a vacuum.
 14. The method of claim 11, furthercomprising: forming a portion of the conductive material into anelectrical connection from the gyroscope inside the packaging to an areaoutside of the packaging.
 15. The method of claim 11, furthercomprising: forming a seal ring, wherein the encapsulating involvesattaching a cover to the seal ring.
 16. The method of claim 15, whereinthe cover includes metal or glass.
 17. The method of claim 15, furthercomprising: forming an electrical pad outside of the seal ring, theelectrical pad being capable of electrical connection with theconductive material.
 18. The method of claim 1, wherein forming theproof mass and forming the drive frame involves: etching between a driveframe area and a proof mass area; depositing high aspect ratiophotoresist material between the drive frame area and the proof massarea; and electroplating a metal layer in the drive frame area and theproof mass area.
 19. The method of claim 18, wherein forming the proofmass and forming the drive frame also involves: removing the high aspectratio photoresist material from between the drive frame area and theproof mass area; etching to expose a sacrificial layer disposed belowthe drive frame and the proof mass; and removing the sacrificial layerto release the drive frame and the proof mass.